Manipulation of non-terminally differentiated cells using the Notch pathway

ABSTRACT

The present invention is directed to methods for the expansion of non-terminally differentiated cells (“precursor cells”) using agonists of Notch function, by inhibiting the differentiation of the cells without inhibiting proliferation (mitotic activity) such that an expanded population of non-terminally differentiated cells is obtained. The cells are preferably stem or progenitor cells. These expanded cells can be used in cell replacement therapy to provide desired cell populations and help in the regeneration of diseased and/or injured tissues. The expanded cell populations can also be made recombinant and used for gene therapy, or can be used to supply functions associated with a particular precursor cell or its progeny cell.

[0001] This invention was made with government support under grant number NS 26084 awarded by the National Institutes of Health. The government has certain rights in the invention.

1. FIELD OF THE INVENTION

[0002] The present invention is directed to methods for the expansion of non-terminally differentiated cells (“precursor cells”) using Notch reagents, by maintaining the differentiation state of the cells without inhibiting proliferation (“mitotic activity”) such that an expanded population of non-terminally differentiated cells is obtained. The cells are preferably stem or progenitor cells. These expanded cells can be used in cell replacement therapy to repopulate lost cell populations and help in the regeneration of diseased and/or injured tissues. The expanded cell populations can also be made recombinant and used for gene therapy, or can be used to supply functions (e.g., expressed protein products) associated with of a particular precursor cell or its progeny cells.

2. BACKGROUND OF THE INVENTION

[0003] The developmental processes that govern the ontogeny of multicellular organisms, including humans, depends on the interplay between signaling pathways, which gradually narrow the developmental potential of cells from the original totipotent stem cell to the terminally differentiated mature cell, which performs a specialized function, such as a heart cell or a nerve cell.

[0004] The fertilized egg is the cell from which all other cell lineages derive, i.e., the ultimate stem cell. As development proceeds, early embryonic cells respond to growth and differentiation signals which gradually narrow the cells' developmental potential, until the cells reach developmental maturity, i.e., are terminally differentiated. These terminally differentiated cells have specialized functions and characteristics, and represent the last step in a multi-step process of precursor cell differentiation into a particular cell.

[0005] The transition from one step to the next in cell differentiation is governed by specific biochemical mechanisms which gradually control the progression until maturity is reached. It is clear that the differentiation of tissues and cells is a gradual process which follows specific steps until a terminally differentiated state is reached.

[0006] Gastrulation, the morphogenic movement of the early embryonic cell mass, results in the formation of three distinct germ cell layers, the ectoderm, the mesoderm, and the endoderm. As cells in each germ cell layer respond to various developmental signals, specific organs are generated which are composed of specific differentiated cells. For example, the epidermis and the nervous system develop from ectoderm-derived cells, the respiratory system and the digestive tract are developed from endoderm-derived cells, and mesoderm-derived cells develop into the connective tissues, the hematopoietic system, the urogenital system, muscle, and parts of most internal organs.

[0007] The following is a brief outline of how ectoderm, endoderm and mesoderm are developed and further, how these three dermal layers give rise to the different tissues of the body. For a general review of development see Scott F. Gilbert, 1991, Developmental Biology, 3rd Edition, Sinauer Associates, Inc., Sunderland Mass.

[0008] The interaction between the dorsal mesoderm and the overlaying ectoderm initiates organogenesis. In this interaction the chordamesoderm directs the ectoderm above it to form the neural tube which will eventually give rise to the brain and the spinal cord. The differentiation of the neural tube into the various regions of the central nervous system is clear at the gross anatomical level where morphogenetic changes shape specific constrictions and bulges to form the chambers of the brain and the spinal cord. At the cellular level, cell migratory events rearrange various groups of cells. The neuroepithelial cells respond to growth and differentiation signals and eventually differentiate into the numerous types of neurons and supportive (glial) cells. Both neural tube and brain are highly regionalized with each specific region serving distinct functional purposes (see FIG. 1). Each cell in this tissue has specific morphological and biochemical characteristics. Differentiated cells are the last step in a lineage where precursor cells responding to developmental cues progress to a more differentiated state until they reach their terminal differentiation state. For example, ependymal cells which are the integral components of the neural tube lining can give rise to precursors which may differentiate into neurons or glia depending on the developmental cues they will receive (Rakic et al., 1982, Neurosci. Rev. 20:429-611).

[0009] The neural crest derives from the ectoderm and is the cell mass from which an extraordinary large and complex number of differentiated cell types are produced. (see Table I), including the peripheral nervous system, pigment cells, adrenal medulla and certain areas of the head cartilage. TABLE I Major Neural Crest Derivatives* Pigment Sensory Autonomic Skeletal and Skeletal and cells nervous system nervous system connective tissue connective tissue TRUNK CREST (INCLUDING CERVICAL CREST) Melanocytes Spinal ganglia Symphathetic Mesenchyme of dorsal Adrenal Xanthophores Some contributions to Superior cervical fin in amphibia medulla (erythrophores) vagal (X) root ganglia ganglion Walls of aortic Type I cells Iridophores Prevertebral ganglia arches of carotid (guanophores) Paravertebral ganglia Connective tissue of body in dermis Adrenal medulla parathyroid Parafollicle epidermis Parasympahtetic (calcitonin- and epidermal Remark's ganglion producing) derivates Pelvic plexus cells of Visceral and enteric thyroid ganglia Some supportive cells Glia (oligodendrocytes) Schwann sheath cells Some contribution to meninges CRANIAL CREST Small, belated Trigeminal (V) Parasympahtetic ganglia Most visceral contribution Facial (VII) root Chary cartilages Glossopharyngeal (IX) Ethmoid Trabeculae carneae (ant.) root (superior Sphenopalatine Contributes cells to ganglia) Submandibular posterior trabeculae, Vagal (X) root (jugular basal plate, para- ganglia) chordal cartilages Supportive cells Odontoblasts Head mesenchyme (membrane bones)

[0010] The fate of neural crest cells will depend on where they migrate and settle during development since the cells will encounter different differentiation and growth signals that govern their ultimate differentiation. The pluripotentiality of neural crest cells is well established (LeDouarin et al., 1975, Proc. Natl. Acad. Sci USA 72:728-732). A single neural crest cell can differentiate into several different cell types. Transplantation experiments of cell populations or single neural crest cells point to the remarkably plastic differentiation potential of these cells. Even though the cell lineages of the various differentiation pathways have not been established to the degree they have in the hematopoietic development, the existence of multi-potential cell precursors, reminiscent to those seen in the hematopoietic system, is well founded.

[0011] The cells covering the embryo after neurulation form the presumptive epidermis. The epidermis consists of several cellular layers which define a differentiation lineage starting from the undifferentiated, mitotically active basal cells to the terminally differentiated non-dividing keratinocytes. The latter cells are eventually shed and constantly replenished by the underlying less differentiated precursors. Psoriasis, a pathogenic condition of the skin results from the exfoliation of abnormally high levels of epidermal cells.

[0012] Skin is not only the derivative of epidermis. Interactions between mesenchymal dermis, a tissue of mesodermal origin and the epidermis at specific sites, result in the formation of cutaneous appendages, hair follicles, sweat glands and apocrine glands. The cell ensemble that produces hairs is rather dynamic in that the first embryonic hairs are shed before birth and replaced by new follicles (vellus). Vellus, a short and silky hair, remains on many parts of the body which are considered hairless, e.g., forehead and eye lids. In other areas vellus can give way to “terminal” hair. Terminal hair can revert into the production of unpigmented vellus, a situation found normally in male baldness.

[0013] The endoderm is the source of the tissues that line two tubes within the adult body. The digestive tube extends throughout the length of the body. The digestive tube gives rise not only to the digestive tract but also to, for example, the liver, the gallbladder and the pancreas. The second tube, the respiratory tube, forms the lungs and part of the pharynx. The pharynx gives rise to the tonsils, thyroid, thymus, and parathyroid glands.

[0014] The genesis of the mesoderm which has also been referred to as the mesengenic process gives rise to a very large number of internal tissues which cover all the organs between the ectodermal wall and the digestive and respiratory tubes. As is the case with all other organs it is the intricate interplay between various intercellular signaling events and the response of non-terminally differentiated precursor cells that will eventually dictate specific cellular identities. To a large degree organ formation depends on the interactions between mesenchymal cells with the adjacent epithelium. The interaction between dermis and epidermis to form, e.g., hairs, has been described above. The formation of the limbs, the gut organs, e.g., liver or pancreas, kidney, teeth, etc., all depend on interactions between specific mesenchymal and epithelial components. In fact, the differentiation of a given epithelium depends on the nature of the adjacent mesenchyme. For example, when lung bud epithelium is cultured alone, no differentiation occurs. However, when lung bud epithelium is cultured with stomach mesenchyme or intestinal mesenchyme, the lung bud epithelium differentiates into gastric glands or villi, respectively. Further, if lung bud epithelium is cultured with liver mesenchyme or bronchial mesenchyme, the epithelium differentiates into hepatic cords or branching bronchial buds, respectively.

[0015] 2.1. Adult Tissues and Precursor Cells

[0016] Embryonic development produces the fully formed organism. The morphologic, i.e., cellular boundaries of each organ are defined and in the juvenile or adult individual the maintenance of tissues whether during normal life or in response to injury and disease, depends on the replenishing of the organs from precursor cells that are capable of responding to specific developmental signals.

[0017] The best known example of adult cell renewal via the differentiation of immature cells is the hematopoietic system. Here, developmentally immature precursors (hematopoietic stem and progenitor cells) respond to molecular signals to gradually form the varied blood and lymphoid cell types.

[0018] While the hematopoietic system is the best understood self renewing adult cellular system it is believed that most, perhaps all, adult organs harbor precursor cells that under the right circumstances, can be triggered to replenish the adult tissue. For example, the pluripotentiality of neural crest cells has been described above. The adult gut contains immature precursors which replenish the differentiated tissue. Liver has the capacity to regenerate because it contains hepatic immature precursors; skin renews itself, etc. Through the mesengenic process, most mesodermal derivatives are continuously replenished by the differentiation of precursors. Such repair recapitulates the embryonic lineages and entails differentiation paths which involve pluripotent progenitor cells.

[0019] Mesenchymal progenitor cells are pluripotent cells that respond to specific signals and adopt specific lineages. For example, in response to bone morphogenic factors, mesenchymal progenitor cells adopt a bone forming lineage. For example, in response to injury, mesodermal progenitor cells can migrate to the appropriate site, multiply and react to local differentiation factors, consequently adopting a distinct differentiation path. It has been suggested that the reason that only a limited tissue repair is observed in adults is because there are too few progenitor cells which can adopt specific differentiation lineages. It is clear that if such progenitor cells could be expanded, then the tissue repair could be much more efficient. An expanded pool of stem and progenitor cells, as well as non-terminally differentiated cells supplying a desired differentiation phenotype, would be of great value in gene therapy and myriad therapeutic regimens.

[0020] 2.2. The Notch Pathway

[0021] Genetic and molecular studies have led to the identification of a group of genes which define distinct elements of the Notch signaling pathway. While the identification of these various elements has come exclusively from Drosophila using genetic tools as the initial guide, subsequent analyses have lead to the identification of homologous proteins in vertebrate species including humans. FIG. 2 depicts the molecular relationships between the known Notch pathway elements as well as their subcellular localization (Artavanis-Tsakonas et al., 1995, Science 268:225-232).

[0022] The extracellular domain of Notch carries 36 EGF-like repeats, two of which have been implicated in interactions with the Notch ligands Serrate and Delta. Delta and Serrate are membrane bound ligands with EGF homologous extracellular domains, which interact physically with Notch on adjacent cells to trigger signaling.

[0023] Functional analyses involving the expression of truncated forms of the Notch receptor have indicated that receptor activation depends on the six cdc10/ankyrin repeats in the intracellular domain. Deltex and Suppressor of Hairless, whose over-expression results in an apparent activation of the pathway, associate with those repeats.

[0024] Deltex is a cytoplasmic protein which contains a ring zinc finger. Suppressor of Hairless on the other hand, is the Drosophila homologue of CBF1, a mammalian DNA binding protein involved in the Epstein-Barr virus-induced immortalization of B cells. It has been demonstrated that, at least in cultured cells, Suppressor of Hairless associates with the cdc10/ankyrin repeats in the cytoplasm and translocates into the nucleus upon the interaction of the Notch receptor with its ligand Delta on adjacent cells (Fortini and Artavanis, 1994, Cell 79:273-282). The association of Hairless, a novel nuclear protein, with Suppressor of Hairless has been documented using the yeast two hybrid system therefore, it is believed that the involvement of Suppressor of Hairless in transcription is modulated by Hairless (Brou et al., 1994, Genes Dev. 8:2491; Knust et al. 1992, Genetics 129:803).

[0025] Finally, it is known that Notch signaling results in the activation of at least certain bHLH genes within the Enhancer of split complex (Delidakis et al., 1991, Genetics 129:803). Mastermind encodes a novel ubiquitous nuclear protein whose relationship to Notch signaling remains unclear but is involved in the Notch pathway as shown by genetic analysis (Smoller et al., 1990, Genes Dev. 4:1688).

[0026] The generality of the Notch pathway manifests itself at different levels. At the genetic level, many mutations exist which affect the development of a very broad spectrum of cell types in Drosophila. Knockout mutations in mice are embryonic lethals consistent with a fundamental role for Notch function (Swiatek et al., 1994, Genes Dev. 8:707). Mutations in the Notch pathway in the hematopoietic system in humans are associated with lymphoblastic leukemia (Ellison et al., 1991, Cell 66:649-661). Finally the expression of mutant forms of Notch in developing Xenopus embryos interferes profoundly with normal development (Coffman et al., 1993, Cell 73:659).

[0027] The expression patterns of Notch in the Drosophila embryo are complex and dynamic. The Notch protein is broadly expressed in the early embryo, and subsequently becomes restricted to uncommitted or proliferative groups of cells as development proceeds. In the adult, expression persists in the regenerating tissues of the ovaries and testes (reviewed in Fortini et al., 1993, Cell 75:1245-1247; Jan et al., 1993, Proc. Natl. Acad. Sci. USA 90:8305-8307; Sternberg, 1993, Curr. Biol. 3:763-765; Greenwald, 1994, Curr. Opin. Genet. Dev. 4:556-562; Artavanis-Tsakonas et al., 1995, Science 268:225-232). Studies of the expression of Notch1, one of three known vertebrate homologues of Notch, in zebrafish and Xenopus, have shown that the general patterns are similar; with Notch expression associated in general with non-terminally differentiated, proliferative cell populations. Tissues with high expression levels include the developing brain, eye and neural tube (Coffman et al., 1990, Science 249:1438-1441; Bierkamp et al., 1993, Mech. Dev. 43:87-100). While studies in mammals have shown the expression of the corresponding Notch homologues to begin later in development, the proteins are expressed in dynamic patterns in tissues undergoing cell fate determination or rapid proliferation (Weinmaster et al., 1991, Development 113:199-205; Reaume et al., 1992, Dev. Biol. 154:377-387; Stifani et al., 1992, Nature Genet. 2:119-127; Weinmaster et al., 1992, Development 116:931-941; Kopan et al., 1993, J. Cell Biol, 121:631-641; Lardelli et al., 1993, Exp. Cell Res. 204:364-372; Lardelli et al., 1994, Mech. Dev. 46:123-136; Henrique et al., 1995, Nature 375:787-790; Horvitz et al., 1991, Nature 351:535-541; Franco del Amo et al., 1992, Development 115:737-744). Among the tissues in which mammalian Notch homologues are first expressed are the pre-somitic mesoderm and the developing neuroepithelium of the embryo. In the pre-somitic mesoderm, expression of Notch1 is seen in all of the migrated mesoderm, and a particularly dense band is seen at the anterior edge of pre-somitic mesoderm. This expression has been shown to decrease once the somites have formed, indicating a role for Notch in the differentiation of somatic precursor cells (Reaume et al., 1992, Dev. Biol. 154:377-387; Horvitz et al., 1991, Nature 351:535-541). Similar expression patterns are seen for mouse Delta (Simske et al., 1995, Nature 375:142-145).

[0028] Within the developing mammalian nervous system, expression patterns of Notch homologue have been shown to be prominent in particular regions of the ventricular zone of the spinal cord, as well as in components of the peripheral nervous system, in an overlapping but non-identical pattern. Notch expression in the nervous system appears to be limited to regions of cellular proliferation, and is absent from nearby populations of recently differentiated cells (Weinmster et al., 1991, Development 113:199-205; Reaume et al., 1992, Dev. Biol. 154:377-387; Weinmaster et al., 1992, Development 116:931-941; Kopan et al., 1993, J. Cell Biol. 121:631-641; Lardelli et al., 1993, Exp. Cell Res. 204:364-372; Lardelli et al., 1994, Mech. Dev. 46:123-136; Henrique et al., 1995, Nature 375:787-790; Horvitz et al., 1991, Nature 351:535-541). A rat Notch ligand is also expressed within the developing spinal cord, in distinct bands of the ventricular zone that overlap with the expression domains of the Notch genes. The spatio-temporal expression pattern of this ligand correlates well with the patterns of cells committing to spinal cord neuronal fates, which demonstrates the usefulness of Notch as a marker of populations of cells for neuronal fates (Henrique et al., 1995, Nature 375:787-790). This has also been suggested for vertebrate Delta homologues, whose expression domains also overlap with those of Notch1 (Larsson et al., 1994, Genomics 24:253-258; Fortini et al., 1993, Nature 365:555-557; Simske et al., 1995, Nature 375:142-145). In the cases of the Xenopus and chicken homologues, Delta is actually expressed only in scattered cells within the Notch1 expression domain, as would be expected from the lateral specification model, and these patterns “foreshadow” future patterns of neuronal differentiation (Larsson et al., 1994, Genomics 24:253-258; Fortini et al., 1993, Nature 365:555-557).

[0029] Other vertebrate studies of particular interest have focused on the expression of Notch homologues in developing sensory structures, including the retina, hair follicles and tooth buds. In the case of the Xenopus retina, Notch1 is expressed in the undifferentiated cells of the central marginal zone and central retina (Coffman et al., 1990, Science 249:1439-1441; Mango et al., 1991, Nature 352:811-815). Studies in the rat have also demonstrated an association of Notch1 with differentiating cells in the developing retina have been interpreted to suggest that Notch1 plays a role in successive cell fate choices in this tissue (Lyman et al., 1993, Proc. Natl. Acad. Sci. USA 90:10395-10399).

[0030] A detailed analysis of mouse Notch1 expression in the regenerating matrix cells of hair follicles was undertaken to examine the potential participation of Notch proteins in epithelial/mesenchymal inductive interactions (Franco del Amo et al., 1992, Development 115:737-744). Such a role had originally been suggested for Notch1 based on the its expression in rat whiskers and tooth buds (Weinmaster et al., 1991, Development 113:199-205). Notch1 expression was instead found to be limited to subsets of non-mitotic, differentiating cells that are not subject to epithelial/mesenchymal interactions, a finding that is consistent with Notch expression elsewhere.

[0031] Expression studies of Notch proteins in human tissue and cell lines have also been reported. The aberrant expression of a truncated Notch1 RNA in human T-cell leukemia results from a translocation with a breakpoint in Notch1 (Ellisen et al., 1991, Cell 66:649-661). A study of human Notch1 expression during hematopoiesis has suggested a role for Notch1 in the early differentiation of T-cell precursors (Mango et al., 1994, Development 120:2305-2315). Additional studies of human Notch1 and Notch2 expression have been performed on adult tissue sections including both normal and neoplastic cervical and colon tissue. Notch1 and Notch2 appear to be expressed in overlapping patterns in differentiating populations of cells within squamous epithelia of normal tissues that have been examined and are clearly not expressed in normal columnar epithelia, except in some of the precursor cells. Both proteins are expressed in neoplasias, in cases ranging from relatively benign squamous metaplasias to cancerous invasive adenocarcinomas in which columnar epithelia are replaced by these tumors (Mello et al., 1994, Cell 77:95-106).

[0032] Insight into the developmental role and the general nature of Notch signaling has emerged from studies with truncated, constitutively activated forms of Notch in several species. These recombinantly engineered Notch forms, which lack extracellular ligand-binding domains, resemble the naturally occurring oncogenic variants of mammalian Notch proteins and are constitutively activated using phenotypic criteria (Greenwald, 1994, Curr. Opin. Genet. Dev. 4:556; Fortini et al., 1993, Nature 365:555-557; Coffman et al., 1993, Cell 73:659-671; Struhl et al., 1993, Cell 69:1073; Rebay et al., 1993, Genes Dev. 7:1949; Kopan et al., 1994, Development 120:2385; Roehl et al., 1993, Nature 364:632).

[0033] Ubiquitous expression of activated Notch in the Drosophila embryo suppresses neuroblast segregation without impairing epidermal differentiation (Struhl et al., 1993, Cell 69:331; Rebay et al., 1993, Genes Dev. 7:1949).

[0034] Persistent expression of activated Notch in developing imaginal epithelia likewise results in an overproduction of epidermis at the expense of neural structures (Struhl et al., 1993, Cell 69:331).

[0035] Neuroblast segregation occurs in temporal waves that are delayed but not prevented by transient expression of activated Notch in the embryo (Struhl et al., 1993, Cell 69:331).

[0036] Transient expression in well-defined cells of the Drosophila eye imaginal disc causes the cells to ignore their normal inductive cues and to adopt alternative cell fates (Fortini et al., 1993, Nature 365:555-557).

[0037] Studies utilizing transient expression of activated Notch in either the Drosophila embryo or the eye disc indicate that once Notch signaling activity has subsided, cells may recover and differentiate properly or respond to later developmental cues (Fortini et al., 1993, Nature 365:555-557; Struhl et al., 1993, Cell 69:331).

[0038] For a general review on the Notch pathway and Notch signaling, see Artavanis-Tsakonas et al., 1995, Science 268:225-232.

[0039] Citation or identification of any reference in Section 2 or any other section of this application shall not be construed as an admission that such reference is available as prior art to the present invention.

3. SUMMARY OF THE INVENTION

[0040] The present invention is directed to methods for the expansion of non-terminally differentiated cells (“precursor cells”) by activating the Notch pathway in a precursor cell such that differentiation of the precursor cell is inhibited without destroying the ability of the cell to proliferate. The precursor cell is preferably a stem or progenitor cell. The present invention is also directed to methods for the expansion of precursor cells in precursor cell containing-populations by activating the Notch pathway in the cells such that the differentiation of the stem cell is inhibited without affecting the mitotic activity of the stem cells. Further, the precursor cells can be isolated from a cell population, if desired, before or after Notch pathway activation. Activation of the Notch pathway is preferably achieved by contacting the cell with a Notch ligand, e.g., in soluble form or recombinantly expressed on a cell surface or immobilized on a solid surface, or by introducing into the cell a recombinant nucleic acid expressing a dominant active Notch mutant or an activating Notch ligand, or other molecule that activates the Notch pathway.

[0041] Activating Notch in the precursor cell renders the precursor cell refractory to differentiation signals, thus substantially inhibiting differentiation and allowing maintenance of the cell in its differentiation stage, and, optionally, expansion of the cell upon exposure to cell growth conditions. Thus, the methods of the invention provide precursor cells of a specific differentiation state. Thus, in one embodiment, such a cell which expresses a desired differentiation phenotype (e.g., production of a desired hormone or growth factor) can be administered to a patient wherein the differentiation phenotype is therapeutically useful (e.g., hormone or growth factor deficiency). Alternatively, an expanded stem or progenitor cell population produced by activation of Notch and cell growth can be used to replace or supplement the stem or progenitor cell lineage in a patient by administration of such cell population. If desired, members of the expanded cell population can be induced to differentiate in vitro prior to in vivo administration, so as to supply to the patient the function of a more differentiated cell population. Preferably, the Notch activation is carried out in vitro and is reversible so that upon in vivo administration of the cells differentiation can occur. Thus, for example, in a preferred embodiment, a Notch ligand is used to activate Notch on the cells, e.g., by being added in soluble form to the cell media, or contacting the cells with a layer of cells in culture expressing the Notch ligand (e.g., Delta, Serrate) on its surface.

[0042] The precursor cells to be expanded in the present invention can be isolated from a variety of sources using methods known to one skilled in the art (see Section 5.5, infra). The precursor cells can be of any animal, preferably mammalian, most preferably human, and can be of primary tissue, cell lines, etc. The precursor cells can be of ectodermal, mesodermal or endodermal origin. Any precursor cells which can be obtained and maintained in vitro can potentially be used in accordance with the present invention. In a preferred embodiment, the precursor cell is a stem cell. Such stem cells include but are not limited to hematopoietic stem cells (HSC), stem cells of epithelial tissues such as the skin and the lining of the gut, embryonic heart muscle cells, and neural stem cells (Stemple and Anderson, 1992, Cell 71:973-985). The stem cells can be expanded under cell growth conditions, i.e., conditions that promote proliferation (“mitotic activity”) of the cells.

[0043] The least differentiated cell in a cell lineage is termed a stem cell. However, stem cell is an operational term. The classic definition of the stem cell is a cell which can divide to produce another stem cell (self-renewal capacity), as well as a cell which can differentiate along multiple specific differentiation paths. It is often the case that a particular cell within a differentiation lineage, has derived from a “less” differentiated parent and can still divide and give rise to a “more” differentiated cellular progeny. FIG. 3 describes diagrammatically hematopoietic development. Totipotent, pluripotent and progenitor stem cells are referred to in the figure.

[0044] A “precursor cell” may or may not divide and can be triggered to adopt a different differentiation state but not necessarily a fully differentiated state, by responding to specific developmental signals.

[0045] The present invention is also directed to methods for use of the expanded precursor cells for use in gene therapy as well as for use in providing desired cell populations, e.g., for regenerating injured and/or diseased tissues. The expanded precursor cell populations can be administered to a patient using methods commonly known to those skilled in the art (see Section 5.8, infra). In other specific embodiments, after Notch activation and expansion, the precursor can be induced to differentiate in vivo, or alternatively in vitro, followed by administration to an individual, to provide a differentiated phenotype to a patient. Additionally, Notch activation and expansion can be carried out in vitro subsequent to in vitro production of a precursor cell of a desired phenotype from a stem or progenitor cell.

[0046] The present invention is also directed to precursor cells containing recombinant genes, such that the gene is inheritable and expressible by the precursor cell or its progeny. These recombinant precursor cells can be transplanted into a patient such that the desired gene is expressed in the patient to alleviate a disease state caused by the lack of or deficient expression of the recombinant gene. The precursor cells can be made recombinant either before or after precursor cell expansion. Methods of tranfecting the nucleic acid encoding the desired gene product such that the precursor cell or its progeny stably expresses the gene product are known to those of skill in the art and are described infra.

4. BRIEF DESCRIPTION OF THE FIGURES

[0047]FIG. 1 is a diagram showing regional specialization during human brain development. (Gilbert, 1991, Developmental Biology, 3rd Edition, Sinauer Associates, Inc., Sunderland Mass., p. 166.)

[0048]FIG. 2 is a schematic diagram of the Notch signaling pathway. The Notch receptor can bind to either Delta or Serrate through its extracellular domain. Ligand binding can result in receptor multimerization that is stabilized by interactions between the intracellular ankyrin repeats of Notch and the cytoplasmic protein Deltex. These events can control the nuclear translocation of the DNA-binding protein Suppressor of Hairless and its known association with the Hairless protein. The transcriptional induction of the Enhancer of Split bHLH genes appears to depend on Notch signaling.

[0049]FIG. 3 is a schematic diagram of the origin of mammalian blood and lymphoid cells. (Gilbert, 1991, Developmental Biology, 3rd Edition, Sinauer Associates, Inc., Sunderland Mass., p. 232).

[0050]FIG. 4 shows the highly conserved ankyrin repeat region of Notch.

[0051] FIGS. 5A-F. Expression of activated Notch and neural differentiation in cone cell precursors of transgenic flies bearing both sev-Notch^(nucl) and the activated Raf construct sE-raf^(torY9). Third-instar larval eye imaginal discs were reacted with mouse monoclonal antibody C17.9C6 directed against the intracellular domain of Notch and rat monoclonal antibody 7E8A10 directed against the neural antigen ELAV and visualized with immunofluorescent secondary antibodies using confocal microscopy. Low (5A-C) and high (5E-F) magnification images of posterior eye disc regions showing nuclear Notch staining (green) in sevenless-expressing cells (5A,D), nuclei expressing ELAV (red) undergoing neural differentiation (5B,E) and corresponding image overlays of both staining patterns (5C,F). The field shown in (5A-C) spans ommatidial rows 10-23, with the posterior margin of the disc visible at the left; nuclei that express Notch protein do not express ELAV. Individual cone cell precursor nuclei of similar developmental ages are labeled ‘N’ in (5D) if they stain for Notch but not ELAV, and are labelled ‘E’ in (5E) if they stain for ELAV but not Notch. Faint ELAV staining (red) was often observed beneath strongly Notch-positive (green) cone cell precursor nuclei; examples are indicated by asterisks in (5E). Optical sectioning revealed that this ELAV staining corresponds to R1,3, 4, 6 and 7 photoreceptor cell precursor nuclei that are located immediately below and partially intercalated with the cone cell precursor nuclei. Identical staining patterns were observed for sev-Notch^(nucl) flies bearing the activated Sevenless tyrosine kinase construct sev-S11 or the activated Ras1 construct sevRas1^(Val12) instead of sE-raf^(torY9) (data not shown).

[0052] FIGS. 6A-B. Co-expression of activated Notch and activated Sevenless proteins in cone cell precursors of sevenless^(d2) flies bearing sev-Notch^(nucl) and sev-S11. Third-instar larval eye imaginal discs were reacted with rat polyclonal antibody Rat5 directed against the intracellular domain of Notch and mouse monoclonal antibody sev150C3 directed against the 60 kD subunit of Sevenless and visualized with immunofluorescent secondary antibodies using confocal microscopy. The sevenless^(d2) allele produces no protein recognized by mAb sev150C3. (6A) Image overlay of two horizontal optical sections collected at slightly different apical levels within the same posterior eye disc quadrant, showing expression of activated Notch (green) in most of the cone cell precursor nuclei and expression of activated Sevenless (purple) in most of the corresponding apical membranes of the cone cell precursor population. The ring-shaped distribution of Sevenless protein in each assembling ommatidium represents the apical microvillar tufts of up to four cone cell precursors and the R7 precursor cell. (6B) Higher magnification image overlay similar to that in (6A), showing a developing ommatidium in which all four cone cell precursor nuclei express Notch (labelled ‘N’) and all or most cone cell precursor apical membrane tufts exhibit strong Sevenless expression (labelled ‘Sev’).

[0053]FIG. 7. Schematic representation of the epistatic relationship between Notch activation and the signalling pathway involving the sevenless receptor tyrosine kinase, Ras1 and Raf during neural induction of the R7 cell precursor in Drosophila. Sevenless protein (Sev) in the R7 cell precursor is activated by binding to its ligand Bride of sevenless (Boss), presented by the adjacent R8 cell, resulting in Ras1 activation presumably via regulation of the activities of its guanine nucleotide exchange factor Son-of-sevenless and its GTPase-activating protein Gap1. Ras1 activation leads to the activation of Raf. This signalling pathway is inhibited by Notch activation at some point downstream of Raf.

5. DETAILED DESCRIPTION OF THE INVENTION

[0054] The present invention is directed to methods for the expansion of non-terminally differentiated cells (“precursor cells”) by activating the Notch pathway in a precursor cell such that the differentiation of the precursor cell is inhibited without destroying the ability of the cell to proliferate. As used herein, “precursor cells” shall mean any non-terminally differentiated cells. The precursor cell is preferably a stem or progenitor cell. The present invention is also directed to methods for the expansion of precursor cells in precursor cell containing-populations by activating the Notch pathway in the cells such that the differentiation of the stem cell is inhibited without affecting the mitotic activity of the cells. Further, the precursor cells can be isolated from a cell population, if desired, before or after Notch pathway activation. Activation of Notch pathway is preferably achieved by contacting the cell with a Notch ligand, e.g., in soluble form or recombinantly expressed on a cell surface or immobilized on a solid surface, or by introducing into the cell a recombinant nucleic acid expressing a dominant active Notch mutant or an activating Notch ligand, or other molecule that activates the Notch pathway.

[0055] Agonists of the Notch pathway are able to activate the Notch pathway at the level of protein-protein interaction or protein-DNA interaction. Agonists of Notch include but are not limited to proteins and derivatives comprising the portions of toporythmic proteins such as Delta or Serrate or Jagged (Lindsell et al., 1995, Cell 80:909-917) that mediate binding to Notch, and nucleic acids encoding the foregoing (which can be administered to express their encoded products in vivo). In a preferred embodiment, the agonist is a protein or derivative or fragment thereof comprising a functionally active fragment such as a fragment of a Notch ligand that mediates binding to a Notch protein. In another preferred embodiment, the agonist is a human protein or portion thereof (e.g., human Delta). In another preferred embodiment the agonist is Deltex or Suppressor of Hairless or a nucleic acid encoding the foregoing (which can be administered to express its encoded product in vivo).

[0056] The Notch pathway is a signal transducing pathway comprising elements which interact, genetically and/or molecularly, with the Notch receptor protein. For example, elements which interact with the Notch protein on both a molecular and genetic basis are, for example, and not by way of limitation, Delta, Serrate and Deltex. Elements which interact with the Notch protein genetically are, for example, and not by way of limitation, Mastermind, Hairless and Suppressor of Hairless.

[0057] Activating Notch function in the precursor cell renders the precursor cell refractory to differentiation signals, thus substantially inhibiting differentiation and allowing maintenance of the cell in its differentiation stage, and, optionally, expansion of the cell upon exposure to cell growth conditions. Thus, the methods of the invention provide precursor cells of a specific differentiation state. Thus, in one embodiment, such a cell which expresses a desired differentiation phenotype (e.g., production of a desired hormone or growth factor) can be administered to a patient wherein the differentiation phenotype is therapeutically useful (e.g., hormone or growth factor deficiency). Alternatively, an expanded stem or progenitor cell population produced by activation of Notch and cell growth can be used to replace or supplement the stem or progenitor cell lineage in a patient by administration of such cell population. If desired, members of the expanded cell population can be induced to differentiate in vitro prior to in vivo administration, so as to supply to the patient the function of a more differentiated cell population. Preferably, the Notch activation is carried out in vitro and is reversible so that upon in vivo administration of the cells differentiation can occur. Thus, for example, in a preferred embodiment, a Notch ligand is used to activate Notch on the dells, e.g., by being added in soluble form to the cell media, or contacting the cells with a layer of cells in culture expressing the Notch ligand (e.g., Delta, Serrate) on its surface.

[0058] The precursor cells to be expanded in the present invention can be isolated from a variety of sources using methods known to one skilled in the art (see Section 5.5, infra). The precursor cells can be of ectodermal, mesodermal or endodermal origin. Any precursor cells which can be obtained and maintained in vitro can potentially be used in accordance with the present invention. In a preferred embodiment, the precursor cell is a stem cell. Such stem cells include but are not limited to hematopoietic stem cells (HSC), stem cells of epithelial tissues such as the skin and the lining of the gut, embryonic heart muscle cells, and neural stem cells (Stemple and Anderson, 1992, Cell 71:973-985). The stem cells can be expanded under cell growth conditions, i.e., conditions that promote proliferation (“mitotic activity”) of the cells.

[0059] The least differentiated cell in a cell lineage is termed a stem cell. However, stem cell is an operational term. The classic definition of the stem cell is a cell which can divide to produce another stem cell (self-renewal capacity), as well as a cell which can differentiate along multiple specific differentiation paths. It is often the case that a particular cell within a differentiation lineage, has derived from a “less” differentiated parent and can still divide and give rise to a “more” differentiated cellular progeny. FIG. 3 describes diagrammatically hematopoietic development. Totipotent, pluripotent and progenitor stem cells are referred to in the figure.

[0060] A “precursor cell” has specific biochemical properties, may or may not divide and can be triggered to adopt a different differentiation state but not necessarily a fully differentiated state, by responding to specific developmental signals.

[0061] The present invention is also directed to methods for use of the expanded precursor cells for use in gene therapy as well as for use in providing desired cell populations and for use in regenerating injured and/or diseased tissues. The expanded precursor cell populations can be administered to a patient using methods commonly known to those skilled in the art (see Section 5.8, infra). In other specific embodiments, after Notch activation and expansion, the precursor cell can be induced to differentiate in vivo, or alternatively in vitro, followed by administration to an individual, to provide a differentiated phenotype to a patient. Additionally, Notch activation and expansion can be carried out in vitro subsequent to in vitro production of a precursor cell of a desired phenotype from a stem or progenitor cell.

[0062] The present invention is also directed to precursor cells expressing recombinant genes, such that the precursor cells express a desired gene. These recombinant precursor cells can be transplanted into a patient such that the desired gene is expressed in the patient to alleviate a disease state caused by the lack of expression of the recombinant gene. The precursor cells can be made recombinant either before or after precursor cell expansion. Methods of tranfecting the nucleic acid encoding the desired gene product such that the precursor cell or its progeny stably expresses the gene product are known to those of skill in the art and are described infra.

[0063] The subject into which the expanded cells or their progeny are introduced, or from which precursor cells can be derived, is preferably an animal, including but not limited to animals such as cows, pigs, horses, chickens, cats, dogs, etc., and is preferably a mammal, and most preferably human.

[0064] In an embodiment of the present invention, the subjects to which the cells are administered are immunocompromised or immunosuppressed or have an immune deficiency. For example, the subject has Acquired Immune Deficiency Syndrome or has been exposed to radiation or chemotherapy regimens for the treatment of cancer, and the subjects are administered hematopoietic or immune precursor cells such that the administered cells perform a needed immune or hematopoietic function.

[0065] Preferably, the expanded precursor cell is originally derived from the subject to which it is administered, i.e., the transplant is autologous.

[0066] For clarity of disclosure, and by way of limitation, the detailed description of the invention is divided into the following sub-sections:

[0067] (i) Notch signaling and stem cell differentiation,

[0068] (ii) Notch activation inhibits the differentiation of stem cells,

[0069] (iii) Activation of the Notch pathway,

[0070] (iv) Notch and terminal differentiation,

[0071] (v) Obtaining precursor cells,

[0072] (vi) Gene therapy,

[0073] (vii) Pharmaceutical compositions,

[0074] (viii) Transplantation.

[0075] 5.1. Notch Signaling and Stem Cell Differentiation

[0076] The progression of a precursor cell to a more mature or differentiated state depends on a combination of signals that ultimately govern the differentiation steps. Specific factors, for example, bone morphogenic factors or the various factors known to be important in hematopoiesis, for example, interleukin-5 or thrombopoietin, together with intercellular and cell-extracellular matrix interactions contribute to the differentiation of a precursor cell along a specific differentiation path.

[0077] The effectors of such contributions are the various signaling pathways which transmit the extracellular signal to the nucleus, ultimately changing transcriptional expression patterns, i.e., genes expressed only in the tissue that is the cells' ultimate fate are switched on and conversely others are switched off, such that, e.g., kidney cells express kidney-specific genes and do not express liver cell-specific proteins. In order for a precursor cell to respond to the various extracellular signals, it must be competent to do so, for example, in order to respond to a soluble factor the cell must express a receptor which can recognize the factor. Tissue competence has been articulated in the classic studies of Waddington, 1940, organisers and Genes, Cambridge University Press, Cambridge, England.

[0078] The present invention is based, at least in part, on the discovery that the Notch signaling pathway is not a pathway that transmits specific developmental signals such that cell differentiation is effected, but rather it controls the competence of a precursor cell to interpret and respond to differentiation signals. The Notch pathway is a general and evolutionarily conserved developmental “switch.” Specifically, when the Notch pathway is activated in precursor cells, the precursor cells are unable to respond to particular differentiation signals but generally the mitotic ability of the precursor cells remains (i.e., the cells can proliferate). The existence of the Notch pathway allows for the manipulation of the differentiation state of precursor cells without knowing all of the differentiation signals, e.g., growth factors, which are required for the maintenance of a particular differentiation state or for advancing the cell to a more differentiated state. In a preferred aspect, the inhibitory effect on differentiation by activating the Notch pathway with a Notch function agonist can be reversed by adding an antagonist of the Notch pathway or diluting out the Notch pathway agonist.

[0079] 5.2. Notch Activation Inhibits the Differentiation of Precursor Cells

[0080] Notch regulates the competence of many different cell types to respond to more specific signals, with the particular cell fates chosen depending upon the developmental history of each cell type and the specific signaling pathways operating within it. When Notch function is activated in a precursor cell (e.g., progenitor or stem cell), the precursor cell can be prevented from differentiating even in the presence of the correct differentiation signals. Once, however, Notch function activation subsides, the cells can respond again to developmental cues. We have shown, using human keratinocytes which have been transfected with activated forms of Notch, that while cells stably expressing activated Notch forms are prevented from differentiating, their proliferation potential is not affected.

[0081] The modulation of Notch pathway activity offers a novel and unique tool to manipulate the fate of precursor cells. A precursor at a given developmental state can be “frozen” into that state by virtue of activating the Notch pathway. Importantly, these cells may be expanded, since Notch signaling activity may not destroy or, preferably, does not substantially impair, their ability to divide. Thus, precursor cells may be expanded, ex vivo in order to provide a source of precursors which are useful in gene therapy as well as tissue repair. Notch agonists are also useful in cases where it is important to maintain a cell in a particular differentiation state in order to provide indefinitely, or for a given period of time, a chemical produced by a cell of that differentiated state, to a particular tissue. In this latter embodiment, for example, it may be desired to activate Notch in the cells administered in vivo for a long period of time (e.g., hours or days) or substantially irreversibly, e.g., by excapsulating the cells with a soluble Notch agonist, or having them recombinantly express a Notch dominant active mutant from a constitutive promoter, respectively.

[0082] An embodiment of the present invention is to treat the desired cell population with agonists of the Notch pathway and then either allow these cells to proliferate in culture before transplanting them back into the appropriate region, or directly transplanting them without necessarily allowing them to proliferate in vitro. Antagonists can be used to reverse or neutralize the action of the Notch-function agonist. For example, and not by way of limitation, a Notch ligand or a molecule that mimics the ligand can be used to keep Notch receptor expressing cells in an “activated” state while withdrawal of the ligand will reverse that effect.

[0083] It is possible in many cases that the simple activation of Notch may not suffice to expand the stem cells ex vivo. Subjecting the cell to growth conditions, e.g., culturing it in the presence of specific growth factors or combinations of growth factors may be necessary, nevertheless, the importance of Notch pathway activation in these events will be essential since the presence of only those factors will generally not be sufficient to maintain those cells in culture without differentiation occurring.

[0084] 5.3. Activation of Notch Function

[0085] An agonist of Notch function is an agent that promotes activation of Notch function. As used herein, “Notch function” shall mean a function mediated by the Notch signaling pathway.

[0086] Notch function activation is preferably carried out by contacting a precursor cell with a Notch function agonist. The agonist of Notch function can be a soluble molecule, recombinantly expressed as a cell-surface molecule, on a cell monolayer with which the precursor cells are contacted, a molecule immobilized on a solid phase. In another embodiment, the Notch agonist can be recombinantly expressed from a nucleic acid introduced into the precursor cells. Notch function agonists of the present invention include Notch proteins and analogs and derivatives (including fragments) thereof; proteins that are other elements of the Notch pathway and analogs and derivatives (including fragments) thereof; antibodies thereto and fragments or other derivatives of such antibodies containing the binding region thereof; nucleic acids encoding the proteins and derivatives or analogs; as well as toporythmic proteins and derivatives and analogs thereof which bind to or otherwise interact with Notch proteins or other proteins in the Notch pathway such that Notch function is promoted. Such agonists include but are not limited to Notch proteins and derivatives thereof comprising the intracellular domain, Notch nucleic acids encoding the foregoing, and proteins comprising toporythmic protein domains that interact with Notch (e.g., the extracellular domain of Delta, Serrate or Jagged). Other agonists include Deltex and Suppressor of Hairless. These proteins, fragments and derivatives thereof can be recombinantly expressed and isolated or can be chemically synthesized.

[0087] In a preferred embodiment the agonist is a protein consisting of at least a fragment (termed herein “adhesive fragment”) of the proteins encoded by toporythmic genes which mediate binding to Notch proteins or adhesive fragments thereof. Toporythmic genes, as used herein, shall mean the genes Notch, Delta, Serrate, Jagged, Suppressor of Hairless and Deltex, as well as other members of the Delta/Serrate/Jagged family or Deltex family which may be identified by virtue of sequence homology or genetic interaction and more generally, members of the “Notch cascade” or the “Notch group” of genes, which are identified by molecular interactions (e.g., binding in vitro, or genetic interactions (as depicted phenotypically, e.g., in Drosophila).

[0088] Vertebrate homologs of Notch pathway elements have been cloned and sequenced. For example, these include Serrate (Lindsell et al., 1995, Cell 80:909-917); Delta (Chitnis et al., 1995, Nature 375:761; Henrique et al., 1995, Nature 375:787-790; Bettenhausen et al., 1995, Development 121:2407); and Notch (Coffman et al., 1990, Science 249:1438-1441; Bierkamp et al., 1993, Mech. Dev. 43:87-100; Stifani et al., 1992, Nature Genet. 2:119-127; Lardelli et al., 1993, Exp. Cell Res. 204:364-372; Lardelli et al., 1994, Mech. Dev. 46:123-136; Larsson et al., 1994, Genomics 24:253-258; Ellisen et al., 1991, Cell 66:649-661; Weinmaster et al., 1991, Development 113:199-205; Reaume et al., 1992, Dev. Biol. 154:377-387; Weinmster et al., 1992, Development 116:931-941; Franco del Amo et al., 1993, Genomics 15:259-264; and Kopan et al., 1993, J. Cell. Biol. 121:631-641).

[0089] In one embodiment, the Notch agonist is expressed from a recombinant nucleic acid. For example, in vivo expression of truncated, “activated” forms of the Notch receptor lacking the extra cellular, ligand binding domain results in gain of function mutant phenotypes. When analyzed at the single cell level, these phenotypes demonstrate that expression of such molecules in progenitor or stem cells, prevents the cells from responding to differentiation signals, thus inhibiting differentiation. It has also been mentioned that this process may be desired to be reversible, since when the activated Notch receptor is no longer expressed the undifferentiated stem cells can respond to differentiation signals and differentiate. Thus, preferably the Notch dominant active mutant is expressed inside the precursor cells from an inducible promoter, such that expression can be induced in vitro for expansion, with the inducer lacking in vivo so that differentiation occurs after administration of the transplanted cells.

[0090] Alternatively, in another embodiment the agonist of Notch function is not a recombinant dominant Notch active mutant.

[0091] Alternatively, in another embodiment, contacting of the precursor cells with a Notch agonist is not done by incubation with other cells recombinantly expressing a Notch ligand on the cell surface (although in other embodiments, this method can be used).

[0092] In another embodiment, the recombinantly expressed Notch agonist is a chimeric Notch protein which comprises the intracellular domain of Notch and the extracellular domain of another ligand-binding surface receptor. For example, a chimeric Notch protein comprising the EGF receptor extracellular domain and the Notch intracellular domain is expressed in a precursor cell. However, the Notch pathway will not be active unless the EGF receptor ligand EGF is contacted with the precursor cell-expressing the chimera. As with the inducible promoter controlling the expression of the truncated form of Notch, the activity of the chimeric Notch protein is reversible; when EGF is removed from the cells, Notch activity will cease and the cell can then differentiate. Notch activity can again be turned on with the addition of the ligand.

[0093] A systematic deletion analysis of the intracellular domain of Notch demonstrates that the Notch sequences that are both necessary and sufficient for the downstream signaling of the Notch receptor are confined to the ankyrin repeats of the intracellular region (Matsuno et al., 1995, Development 121:2633-2644 and unpublished results). Using the yeast two hybrid system it was discovered that the ankyrin repeats interact homotypically.

[0094] Expression of appropriate deletion constructs in the defined cellular environment of the developing Drosophila eye demonstrates that expression of a polypeptide fragment comprising just the ankyrin repeats resulted in an activated phenotype. Not surprisingly this is the part of the Notch protein which is most highly conserved among various species. FIG. 4 shows the high sequence homology of ankyrin repeats across evolution.

[0095] These findings suggest that any small molecules, for example, but not by way of limitation, polypeptides or antibodies which bind to the Notch ankyrin repeats, can block its function, and hence behave as antagonists of the pathway. Conversely, molecules that mimic the Notch ankyrin repeat activity can behave as agonists of the Notch pathway. Since the expression of truncated forms of Notch give mutant phenotypes in the developing Drosophila eye, genetic screens for modifiers of these phenotypes can be used for identifying and isolating additional gene products that can act as agonists or antagonists of the pathway.

[0096] Genes that act as enhancers of the activated phenotypes are potential agonists and those that act as suppressors are potential antagonists.

[0097] Deltex and Suppressor of Hairless are also agonists of Notch function that can be used. It has been shown that the activation of the Notch pathway, as judged by the induction of activated phenotypes similar to those induced by the expression of activated forms of Notch, can be achieved by manipulating the expression of Deltex (Schweisguth and Posakony, 1994, Development 120:1477), as well as Suppressor of Hairless (Matsuno et al., 1995, Development 121:2633) both of which can interact with the ankyrin repeats of Notch.

[0098] Using the yeast ‘interaction trap’ assay (Zervos et al., 1993, Cell 72:223-232), as well as cell culture co-localization studies, the protein regions responsible for heterotypic interactions between Deltex and the intracellular domain of Notch, as well as homotypic interaction among Deltex molecules were defined. The function of the Deltex-Notch interaction domains was examined by in vivo expression studies. Taken together, data from over-expression of Deltex fragments and from studies of physical interactions between Deltex and Notch demonstrate that Deltex positively regulates the Notch pathway through interactions with the Notch ankyrin repeats.

[0099] Experiments involving cell cultures indicate that the Deltex-Notch interaction prevents the cytoplasmic retention of Suppressor of Hairless protein, which is normally sequestered in the cytoplasm via association with the Notch ankyrin repeats and translocates to the nucleus when Notch binds to its ligand, Delta. On the basis of these findings Deltex appears to regulate Notch activity by antagonizing the interaction between Notch and Suppressor of Hairless. The translocation of the normally cytoplasmic Suppressor of Hairless protein to the nucleus when Notch binds to a ligand (Fortini and Artavanis-Tsakonas, 1994, Cell 79:273-282) is a convenient assay to monitor for Notch function as well as for the ability of Notch agonists of the present invention to activate Notch function.

[0100] Suppressor of Hairless has been shown to be a DNA binding protein. Genetic and molecular data indicate that the activity of Suppressor of Hairless can be influenced by its binding to the nuclear protein Hairless. Moreover it appears that the transcription of at least some of the bHLH genes of the Enhancer of split complex depends directly on Notch signaling and the ability of Suppressor of Hairless to recognize the appropriate binding sites upstream of these genes. Manipulation of these various interactions (e.g., disrupting the interaction between Notch and Suppressor of Hairless with an antibody directed against the ankyrin repeats) will result in modulating the activity of the Notch pathway.

[0101] Finally, the Notch pathway can be manipulated by the binding of Notch ligands (e.g., Delta, Serrate) to the extracellular portion of the Notch receptor. Notch signaling appears to be triggered by the physical interaction between the extracellular domains of Notch and its membrane-bound ligands on adjacent cells. The expression of full length ligands on one cell triggers the activation of the pathway in the neighboring cell which expresses the Notch receptor. Not surprisingly, the ligands act as agonists of the pathway. On the other hand, the expression of truncated Delta or Serrate molecules which lack intracellular domains expressed in neighboring cells results in non-autonomous, dominant negative phenotypes. This demonstrates that these mutant forms of the receptor act as antagonists of the pathway.

[0102] The definition of the various molecular interactions among the Notch pathway elements provides additional specific pharmacological targets and assays which can be used to screen for Notch function agonists and antagonists. Having evaluated the consequences of a particular molecular manipulation in vivo, this information can be used to design biochemical in vitro screening assays for biological or pharmaceuticals that interfere or enhance Notch function.

[0103] Screening for molecules that will trigger the dissociation of the Notch ankyrin repeats with Suppressor of Hairless and the subsequent translocation of Suppressor of Hairless from the cytoplasm to the nucleus results in the identification of agonists. The activation of transcription of a reporter gene which has been engineered to carry several Suppressor of Hairless binding sites at its 5′ end in a cell that expresses Notch also results in the identification of agonists of the pathway.

[0104] Reversing the underlying logic of these assays leads to the identification of antagonists. For example, cell lines expressing the aforementioned reporter gene can be treated with chemicals and biologicals and those which have the capacity to stop the expression of the reporter gene can be identified.

[0105] The precursor cell in which Notch function has been activated is subjected to cell growth conditions to induce proliferation. Such cell growth conditions (e.g., cell culture medium, temperature, if growth is done in vitro) can be any of those commonly known in the art. Preferably, both Notch activation and exposure to cell growth conditions is carried out in vitro. Contacting the cell with a Notch function agonist and exposing the cell to cell growth conditions can be carried out concurrently or, if the agonist acts over a sufficient period of time, sequentially (as long as Notch function activation to inhibit differentiation is present while cell growth occurs).

[0106] 5.3.1. Modulating Other Signaling Pathways with Notch

[0107] Notch defines a general cell interaction mechanism whose biological function is to permit or block the action of developmental signals that are essential for the progression of undifferentiated progenitor cells to a more differentiated state. Consistent with that is the discovery that one can modulate the activity of other signaling pathways by modulating Notch. Thus, in another embodiment, the invention provides methods of modulating other cell signal transduction pathway, e.g., those that mediate cell growth and differentiation.

[0108] A dramatic example of how Notch signaling regulates specific differentiation pathways involves the Ras pathway in the developing Drosophila eye, which is used to transmit an inductive signal generated by ligand-induced activation of the Sevenless receptor tyrosine kinase, and is blocked by appropriately timed activation of the Notch pathway. We have demonstrated that in the cone cell precursors of the developing Drosophila eye, Notch activation and Ras1-mediated signalling separately cause opposite cell-fate alterations. Co-expression studies in these cells demonstrate that Notch activation inhibits the neural differentiation produced by constitutively activated components of a well-defined inductive signalling cascade, including the Sevenless receptor tyrosine kinase, Ras1 and Raf. Therefore, the activation of Notch in a cell blocks the action of activated ras (see Section 6, infra).

[0109] Consistent with the notion that Notch activation initiates a distinct signalling pathway that modulates the cellular response to signals transduced by diverse pathways is the finding that the modulation of Notch activity controls the action of Drosophila wingless (Hing et al., 1994, Mech. Dev. 47:261-268), a homologue of the mouse wnt-1 locus, which encodes a secreted protein involved in cell-signaling during various stages in development (Nusslein-Volhard and Wieschaus, 1980, Nature 287:795-801; Martinez Arias et al., 1988, Development 103:157-170; Nusse and Varmus, 1992, Cell 69:1073-1087; Struhl and Basler, 1993, Cell 72:527-540). Therefore, agonists and antagonists of the Notch pathway provide a novel and unique tool in manipulating the activity of specific signals which control the differentiation of cells using pathways unrelated to Notch. In a particular embodiment of the invention, cells are contacted with an agonist of Notch function to inhibit the function of a signaling pathway that regulates cell growth or differentiation.

[0110] 5.4. Notch and Terminal Differentiation

[0111] The present invention is also directed to using agents to inhibit the Notch pathway such that cells, which are maintained in one differentiation state by Notch pathway activity, can be allowed to change their differentiation state. Notch expression is generally associated with non-terminally differentiated cells. One exception to this general rule is that Notch is expressed in post-mitotic neurons of rat and human adult retina (Ahmad et al., unpublished results). Immunocytochemical staining data indicates that the Notch polypeptides recognized by the antibodies are nuclear. The expression of engineered Notch fragments that are localized in the nuclear has been documented (reviewed in Artavanis-Tsakonas et al., 1995, Science 268:225-232), and these fragments were shown to be associated with activated mutant phenotypes. The presence of an activated form of Notch in the nucleus may lock these cells into a particular state of differentiation by restricting or completely blocking their capacity to respond to differentiation and/or proliferation stimuli. Therefore, it is conceivable that these post-mitotic neurons maintain their differentiated state by virtue of an activated Notch-1 form that is independent of Notch ligands. This state may perhaps afford such cell populations a certain plasticity. For example, an eventual cessation of nuclear Notch-1 activity might allow these cells to re-enter a mitotic state and/or respond to specific differentiation signals. In this context, it is interesting to note that retinal neurons in lower vertebrates such as Goldfish and Xenopus have regenerative capacity. Chemical ablation of specific neurons, such as degeneration of dopaminergic amacrine cells by 6-OH dopamine result in their replacement by regeneration (Reh and Tully, 1986, Dev. Biol. 114(2):463-469). However, such plasticity for regenerative purposes have not been observed in higher vertebrates. The observed Notch-1 activity in mature retinal neurons in the rat may represent the recapitulation of the functional significance of Notch-1 in-retinal regeneration in lower vertebrates. The invention thus provides a method comprising antagonizing Notch function to confer regenerative properties on the mammalian neurons (e.g., of the central nervous system), thus leading to regeneration. Such a method comprises contacting a mammalian neuron with an antagonist of Notch function and exposing the neuron to neuronal cell growth conditions.

[0112] 5.5. Obtaining Precursor Cells

[0113] Precursor cells can be obtained by any method known in the art. The cells can be obtained directly from tissues of an individual or from cell lines or by production in vitro from less differentiated precursor cells, e.g., stem or progenitor cells. An example of obtaining precursor cells from less differentiated cells is described in Gilbert, 1991, Developmental Biology, 3rd Edition, Sinauer Associates, Inc., Sunderland Mass. Briefly, progenitor cells can be incubated in the presence of other tissues or growth and differentiation factors which cause the cell to differentiate. For example, when lung bud epithelium is cultured alone, no differentiation occurs. However, when lung bud epithelium is cultured with stomach mesenchyme or intestinal mesenchyme, the lung bud epithelium differentiates into gastric glands or villi, respectively. Further, if lung bud epithelium is cultured with liver mesenchyme or bronchial mesenchyme, the epithelium differentiates into hepatic cords or branching bronchial buds, respectively. Once a progenitor cell has reached a desired differentiation state, a Notch function agonist can be used to stop differentiation.

[0114] 5.5.1. Isolation of Stem or Progenitor Cells

[0115] The following describes approaches which allow for the isolation of precursor cells and precursor cell-containing tissues, which are to be treated with agonists and, if subsequently desired, antagonists of the Notch pathway according to the present invention. As already alluded to, isolated cell types or even mixtures of cell populations can be treated with Notch function agonists. The isolated precursor cell or precursor cell population can be cultured ex vivo for proliferation which under the influence of the Notch function agonists and cell growth conditions can continue to divide, i.e., expand, in order to reach the desired numbers before transplantation. Optionally, a recombinant gene can be introduced into the cell so that it or its progeny expresses a desired gene product before transplantation. Introduction of a recombinant gene can be accomplished either before or after precursor cell expansion.

[0116] In a preferred embodiment, the precursor cell populations are purified or at least highly enriched. However, in order to treat precursor cells with Notch reagents it is not necessary that the precursor cells are a pure population. Once a mixture is treated, only Notch pathway-expressing non-differentiated precursors will be refractory to differentiation signals but will respond to growth signals while their differentiated partners will eventually terminally differentiate and cease growing, such that the precursor cells will outgrow the differentiated cells and can be purified from the original mixed population. Consequently, the precursor population can still be expanded selectively. Furthermore, purification may not be necessary or desirable prior to therapeutic administration in vivo.

[0117] The isolation of precursor cells for use in the present invention can be carried out by any of numerous methods commonly known to those skilled in the art. For example, one common method for isolating precursor cells is to collect a population of cells from a patient and using differential antibody binding, wherein cells of one or more certain differentiation stages are bound by antibodies to differentiation antigens, fluorescence activated cell sorting is used to separate the desired precursor cells expressing selected differentiation antigens from the population of isolated cells. The following section describes exemplary methods for the isolation of various types of stem cells.

[0118] 5.5.1.1. Mesenchymal Stem Cells

[0119] One of the most important type of progenitor cells vis a vis for therapeutic applications are those derived from the mesenchyme. Mesenchymal progenitors give rise to a very large number of distinct tissues (Caplan, 1991, J. Orth. Res 641-650). Most work to date involves the isolation and culture of cells which can differentiate into chondrocytes and osteoblasts. The systems developed to isolate the relevant progenitor cell populations were worked out first in chick embryos (Caplan, 1970, Exp. Cell. Res. 62:341-355; Caplan, 1981, 39th Annual Symposium of the Society for Developmental Biology, pp. 37-68; Caplan et al., 1980, Dilatation of the Uterine Cervix 79-98; DeLuca et al., 1977, J. Biol. Chem. 252:6600-6608; Osdoby et al., 1979, Dev. Biol. 73:84-102; Syftestad et al., 1985, Dev. Biol. 110:275-283). Conditions were defined under which chick mesenchymal cells differentiated into chondrocytes and bone. Id. With regard to cartilage and bone, the properties of mouse or human mesenchymal limb appear to be quite similar if not identical (Caplan, 1991, J. Orth. Res. 641-650). Mesenchymal cells capable of differentiating into bone and cartilage have also been isolated from marrow (Caplan, 1991, J. Orth. Res. 641-650).

[0120] Caplan et al., 1993, U.S. Pat. No. 5,226,914 describes an exemplary method for isolating mesenchymal stem cells from bone marrow. These isolated marrow stem cells can be used in conjunction with Notch reagents to expand the stem cell population. These expanded cells may then be transplanted into a host where they can differentiate into osteocytes, cartilage, chondocytes, adipocytes, etc., depending on the surrounding microenvironment of the transplant site.

[0121] Animal models involving mice, rats as well as avian preparations, have suggested that the source for mesenchymal stem cells is bone marrow. It has been possible to purify marrow mesenchymal cells by their differential adhesion to culture dishes and demonstrate that they can differentiate, e.g., into osteoblasts. Expansion of such isolated stem cells using Notch reagents can provide a source of cells which when transplanted to the appropriate sites will be induces by the microenvironment to differentiate into the appropriate lineage and help repair damaged and/or diseased tissue. It is expected that the animal models described to date will be applicable to humans. Indeed, as far as cartilage and bone are concerned, the properties of mouse and human limb mesenchymal cells in culture are quite similar, if not identical (Hauska, 1974, Dev. Biol. 37:345-368; Owens and Solursh, 1981, Dev. Biol. 88:297-311). The isolation of human marrow and the demonstration that cells deriving from it can sustain osteogenesis has been described, e.g., by Bab et al., 1988, Bone Mineral 4:373-386.

[0122] Several bone marrow isolation protocols have been reported and can be used to obtain progenitor or precursor cells. Single cell suspensions from rat bone marrow can be prepared according to Goshima et al., 1991, Clin. Orth. and Rel. Res. 262:298-311. Human stem cell cultures from marrow can be prepared as described by Bab et al., 1988, Bone Mineral 4:373-386 as follows: Whole marrow cells are obtained from five patients. The marrow samples are separated from either the iliac crest or femoral midshaft. Marrow samples, 3 ml in volume, are transferred to 6 ml of serum-free Minimal Essential Medium (MEM) containing 50 U/ml penicillin and 0.05 mg/ml streptomycin-sulfate. A suspension of predominantly single cells is prepared as described previously (Bab et al., 1984, Calcif. Tissue Int. 36:77-82; Ashton et al., 1984, Calcif. Tissue Int. 36:83-86) by drawing the preparation into a syringe and expelling it several times sequentially through 19, 21, 23 and 25 gauge needles. The cells are counted using a fixed volume hemocytometer and the concentration adjusted to 1-5×10⁸ total marrow cells per ml suspension. Positive and negative control cell suspensions can be set as described before (Shteyer et al., 1986, Calcif. Tissue Int. 39:49-54), using rabbit whole marrow and spleen cells, respectively.

[0123] 5.5.1.2. Neural Stem Cells

[0124] It is generally assumed that neurogenesis in the central nervous system ceases before or soon after birth. In recent years, several studies have presented evidence indicating that at least to some degree new neurons continue to be added to the brain of adult vertebrates (Alvarez-Buylla and Lois, 1995, Stem Cells (Dayt) 13:263-272). The precursors are generally located in the wall of the brain ventricles. It is thought that from these proliferative regions, neuronal precursors migrate towards target positions where the microenvironment induces them to differentiate. Studies have been reported where cells from the sub-ventricular zone can generate neurons both in vivo as well as in vitro, reviewed in Alvarez-Buylla and Lois, 1995, Stem Cells (Dayt) 13:263-272.

[0125] The neuronal precursors from the adult brain can be used as a source of cells for neuronal transplantation (Alvarez-Buylla, 1993, Proc. Natl. Acad. Sci. USA 90:2074-2077). Neural crest cells have also been long recognized to be pluripotent neuronal cells which can migrate and differentiate into different cell neuronal cell types according to the instructions they receive from the microenvironment they find themselves in (LeDouarin and Ziller, 1993, Curr. Opin. Cell Biol. 5:1036-1043).

[0126] 5.5.1.3. Fetal Cells

[0127] The fact that fetal brain tissue has been shown to have clear behavioral effects when transplanted into adult lesioned brains, has focused attention on human fetal tissue as a potential cell source in transplantation protocols designed to improve neurodegenerative disorders (Bjorklund, 1993, Nature 362:414-415; McKay, 1991, Trends Neurosci. 14:338-340). Nevertheless both ethical, as well as practical considerations make fetal tissue a difficult source to deal with. Expansion of neuronal stem cells whether fetal or otherwise using Notch function agonists provides an alternative source for obtaining the desired quantities of precursor cells for transplantation purposes. Fetal tissues or adult tissues containing precursors can be treated with Notch function agonists as described earlier in order to expand the undifferentiated progenitor cell populations. Fetal cells can placed into primary culture using, for example, protocols developed by Sabate et al., 1995, Nature Gen. 9:256-260, before being treated with Notch function agonists. By way of example but not limitation, the procedure is as follows: Primary cultures of human fetal brain cells can be isolated from human fetuses, obtained from legal abortions after 5 to 12 weeks of gestation. Expulsion can be done by syringe-driven gentle aspiration under echographic control. Fetuses collected in sterile hibernation medium are dissected in a sterile hood under a stereomicroscope. Brains are first removed in toto in hibernation medium containing penicillin G 500 U/ml, streptomycin 100 μg/ml, and fungizon 5 pg/ml. For fetuses of six to eight weeks of age the brain is separated into an anterior (telencephalic vesicles and diencephalon) and a posterior fraction (mesencephalon, pons and cerebellar enlage) and a posterior in toto after careful removal of meninges. For older fetuses, striatal hippocampal, cortical and cerebellar zones expected to contain proliferative precursor cells are visualized under the stereomicroscope and dissected separately. Cells are transferred to either Opti-MEM (Gibco BRL) containing 15% heat-inactivated fetal bovine serum (FBS) (Seromed), or to a defined, serum-free medium (DS-FM) with human recombinant bFGF (10 ng/ml, Boehringer), which is a minor modification of the Bottenstein-Sato medium 39 with glucose, 6 g/l, glutamine 2 mM (Gibco BRL), insulin 25 ug/ml (Sigma) transferrin 100 μg/ml (Sigma), sodium selenite 30 nM (Gibco BRL), progesterone 20 nM (Sigma), putrescine 60 nM (Sigma), penicillin G (500 U/ml), streptomycin 100 μg/ml, and fungizon 5 μg/ml. Cells, approximately 40,000 per cm², are grown at 37° C. in an atmosphere containing 10% CO₂ in tissue culture dishes (Falcon or Nunc) coated with gelatin (0.25% wt/vol) followed by Matrigel (Gibco BRL, a basement membrane extract enriched in laminin and containing trace amounts of growth factors diluted one in 20). Cells in culture can be treated with Notch function agonists in order to expand the population of the appropriate cells until the desired cell mass is reached for transplantation.

[0128] 5.5.1.4. Hematopoietic Stem Cells

[0129] Any technique which provides for the isolation, propagation, and maintenance in vitro of hematopoietic stem cells (HSC) can be used in this embodiment of the invention. Techniques by which this can be accomplished include (a) the isolation and establishment of HSC cultures from bone marrow cells isolated from the future host, or a donor, or (b) the use of previously established long-term HSC cultures, which may be allogeneic or xenogeneic. Non-autologous HSC are used preferably in conjunction with a method of suppressing transplantation immune reactions of the future host/patient. In a particular embodiment of the present invention, human bone marrow cells can be obtained from the posterior iliac crest by needle aspiration (see, e.g., Kodo et al., 1984, J. Clin. Invest. 73:1377-1384). In a preferred embodiment of the present invention, the HSCs can be made highly enriched or in substantially pure form. This enrichment can be accomplished before, during, or after long-term culturing, and can be done by any techniques known in the art. Long-term cultures of bone marrow cells can be established and maintained by using, for example, modified Dexter cell culture techniques (Dexter et al., 1977, J. Cell Physiol. 91:335) or Witlock-Witte culture techniques (Witlock and Witte, 1982, Proc. Natl. Acad. Sci. USA 79:3608-3612).

[0130] Another technique for the isolation of HSC is described by Milner et al., 1994, Blood 83:2057-2062. Bone marrow samples are obtained and are separated by Ficoll-Hypaque density gradient centrifugation, are washed, and stained using two-color indirect immunofluorescent antibody binding and then separated by fluorescence-activated cell sorting (FACS). The cells are labelled simultaneously with IgG antibodies such that CD34⁺ hematopoietic stem cells, including the immature subset that lacks expression of individual lineage associated antigens, CD34⁺lin⁻, are isolated from the cells collected from marrow.

[0131] Where hematopoietic progenitor cells are desired, the presence of hematopoietic progenitor cells and/or their progeny can be detected by commonly known in vitro colony forming assays (e.g., those that detect CFU-GM, BFU-E). As another example, assays for hematopoietic stem cells are also known in the art (e.g., spleen focus forming assays, assays that detect the ability to form progenitors after replating).

[0132] 5.5.1.5. Epithelial Stem Cells

[0133] Epithelial stem cells (ESCs) or keratinocytes can be obtained from tissues such as the skin and the lining of the gut by known procedures (Rheinwald, 1980, Meth. Cell Bio. 21A:229). In stratified epithelial tissue such as the skin, renewal occurs by mitosis of precursor cells within the germinal layer, the layer closest to the basal lamina. Precursor cells within the lining of the gut provide for a rapid renewal rate of this tissue. ESCs or keratinocytes obtained from the skin or lining of the gut of a patient or donor can be grown in tissue culture (Rheinwald, 1980, Meth. Cell Bio. 21A:229; Pittelkow and Scott, 1986, Mayo Clinic Proc. 61:771). If the ESCs are provided by a donor, a method for suppression of host versus graft reactivity (e.g., irradiation, drug or antibody administration to promote moderate immunosuppression) can also be used.

[0134] 5.5.1.6. Liver Stem Cells

[0135] Liver stem cells can be isolated by methods described in PCT Publication WO 94/08598, dated Apr. 28, 1994.

[0136] 5.5.1.7. Kidney Stem Cells

[0137] Mammalian kidney emerges from the metanephric mesenchyme which induces the uteric bud to undergo a series of morphogenetic movements ultimately forming the mature urinary collecting system (Nigam and Brenner, 1992, Curr. Opin. Nephrol. Huper 1:187-191. The uteric bud, an epithelial outgrowth of the Wolfian duct, contracts and induces condensing adjacent mesenchyme along differentiation pathways of epithelial divergence in early embryonic life. Attempts to study this process in vitro have been reported; metanephros in organ culture can be induced to form tubules using embryonic spinal cord as the inducer. While the specific transducing agents that lead to the induction of metanephric mesenchyme by the uteric bud in vivo or by spinal cord in vitro are not known, it is clear that differentiation program is induced in progenitor cells (Karp et al., 1994, Dev. Biol. 91:5286-5290).

[0138] 5.5.2. Expansion and Differentiation

[0139] After the precursors cells have been isolated according to the methods described above or other methods known in the art, the precursor cells can be contacted with an amount of an agonist of Notch function effective to inhibit differentiation, and are exposed to cell growth conditions (e.g., promoting mitosis) such that the cell proliferates to obtain an expanded precursor population according to the present invention.

[0140] In one embodiment, substantially no differentiation of the precursor cells occurs during expansion. The amount of differentiation that occurs can be assayed for by known assays, e.g., those that detect the presence of more differentiated cells by detecting functions associated with a particular stage of differentiation, e.g., expression of differentiation antigens on the cell surface or secretion of proteins associated with a particular state, or ability to generate various cell types, or detecting morphology associated with particular stages of differentiation.

[0141] Once the population has reached a desired titer, the Notch function agonist can be removed (e.g., by separation, dilution), or a Notch function antagonist can be added, such that Notch function is absent or inhibited allowing at least some of the cells in the expanded population to differentiate in the presence of the desired differentiation signals to a desired differentiation state or to a differentiation state of the cell such that the cell expresses a desired phenotype. Optionally, once the cells reach the desired differentiation state the Notch pathway can again be activated with a Notch agonist to freeze the cell in that differentiation state. The cells can be differentiated to a terminally differentiated state if the function of that terminally differentiated cell is desired.

[0142] 5.6. Gene Therapy

[0143] The cells produced by manipulation of the Notch pathway can be made recombinant and used in gene therapy. In its broadest sense, gene therapy refers to therapy performed by the administration of a nucleic acid to a subject. The nucleic acid, either directly or indirectly via its encoded protein, mediates a therapeutic effect in the subject. The present invention provides methods of gene therapy wherein a nucleic acid encoding a protein of therapeutic value (preferably to humans) is introduced into the precursor cells expanded according to the invention, before or after expansion, such that the nucleic acid is expressible by the precursor cells and/or their progeny, followed by administration of the recombinant cells to a subject.

[0144] The recombinant precursor cells of the present invention can be used in any of the methods for gene therapy available in the art. Thus, the nucleic acid introduced into the cells may encode any desired protein, e.g., a protein missing or dysfunctional in a disease or disorder. The descriptions below are meant to be illustrative of such methods. It will be readily understood by those of skill in the art that the methods illustrated represent only a sample of all available methods of gene therapy.

[0145] For general reviews of the methods of gene therapy, see Goldspiel et al., 1993, Clinical Pharmacy 12:488-505; Wu and Wu, 1991, Biotherapy 3:87-95; Tolstoshev, 1993, Ann. Rev. Pharmacol. Toxicol. 32:573-596; Mulligan, 1993, Science 260:926-932; and Morgan and Anderson, 1993, Ann. Rev. Biochem. 62:191-217; May, 1993, TIBTECH 11(5):155-215). Methods commonly known in the art of recombinant DNA technology which can be used are described in Ausubel et al. (eds.), 1993, Current Protocols in Molecular Biology, John Wiley & Sons, NY; and Kriegler, 1990, Gene Transfer and Expression, A Laboratory Manual, Stockton Press, NY.

[0146] In an embodiment in which recombinant precursor cells are used in gene therapy, a gene whose expression is desired in a patient is introduced into the precursor cells such that it is expressible by the cells and/or their progeny, and the recombinant cells are then administered in vivo for therapeutic effect.

[0147] Precursor cells or expanded precursor cells can be used in any appropriate method of gene therapy, as would be recognized by those in the art upon considering this disclosure. The resulting action of a recombinant precursor cell or its progeny cells administered to a patient can, for example, lead to the activation or inhibition of a pre-selected gene in the patient, thus leading to improvement of the diseased condition afflicting the patient.

[0148] The desired gene is transferred to precursor cells in tissue culture by such methods as electroporation, lipofection, calcium phosphate mediated transfection, or viral infection. Usually, the method of transfer includes the transfer of a selectable marker to the cells. The cells are then placed under selection to isolate those cells that have taken up and are expressing the transferred gene. Those precursor cells are then delivered to a patient.

[0149] In this embodiment, the desired gene is introduced into a precursor cell prior to administration in vivo of the resulting recombinant cell. Such introduction can be carried out by any method known in the art, including but not limited to transfection, electroporation, microinjection, infection with a viral or bacteriophage vector containing the gene sequences, cell fusion, chromosome-mediated gene transfer, microcell-mediated gene transfer, spheroplast fusion, etc. Numerous techniques are known in the art for the introduction of foreign genes into cells (see e.g., Loeffler and Behr, 1993, Meth. Enzymol. 217:599-618; Cohen et al., 1993, Meth. Enzymol. 217:618-644; Cline, 1985, Pharmac. Ther. 29:69-92) and may be used in accordance with the present invention, provided that the necessary developmental and physiological functions of the recipient cells are not disrupted. The technique should provide for the stable transfer of the gene to the cell, so that the gene is expressible by the cell and preferably heritable and expressible by its cell progeny.

[0150] One common method of practicing gene therapy is by making use of retroviral vectors (see Miller et al., 1993, Meth. Enzymol. 217:581-599). A retroviral vector is a retrovirus that has been modified to incorporate a preselected gene in order to effect the expression of that gene. It has been found that many of the naturally occurring DNA sequences of retroviruses are dispensable in retroviral vectors. Only a small subset of the naturally occurring DNA sequences of retroviruses is necessary. In general, a retroviral vector must contain all of the cis-acting sequences necessary for the packaging and integration of the viral genome. These cis-acting sequences are:

[0151] a) a long terminal repeat (LTR), or portions thereof, at each end of the vector;

[0152] b) primer binding sites for negative and positive strand DNA synthesis; and

[0153] c) a packaging signal, necessary for the incorporation of genomic RNA into virions.

[0154] The gene to be used in gene therapy is cloned into the vector, which facilitates delivery of the gene into a precursor cell by infection or delivery of the vector into the cell.

[0155] More detail about retroviral vectors can be found in Boesen et al., 1994, Biotherapy 6:291-302, which describes the use of a retroviral vector to deliver the mdr1 gene to hematopoietic stem cells in order to make the stem cells more resistant to chemotherapy. Other references illustrating the use of retroviral vectors in gene therapy are: Clowes et al., 1994, J. Clin. Invest. 93:644-651; Kiem et al., 1994, Blood 83:1467-1473; Salmons and Gunzberg, 1993, Human Gene Therapy 4:129-141; and Grossman and Wilson, 1993, Curr. Opin. in Genetics and Devel. 3:110-114.

[0156] Adenoviruses are also of use in gene therapy. Adenoviruses are especially attractive vehicles for delivering genes to respiratory precursor cells. Adenoviruses can also be used to deliver genes to precursor cells from the liver, the central nervous system, endothelium, and muscle. Adenoviruses have the advantage of being capable of infecting non-dividing cells. Kozarsky and Wilson, 1993, Current Opinion in Genetics and Development 3:499-503 present a review of adenovirus-based gene therapy. Other instances of the use of adenoviruses in gene therapy can be found in Rosenfeld et al., 1991, Science 252:431-434; Rosenfeld et al., 1992, Cell 68:143-155; and Mastrangeli et al., 1993, J. Clin. Invest. 91:225-234.

[0157] It has been proposed that adeno-associated virus (AAV) be used in gene therapy (Walsh et al., 1993, Proc. Soc. Exp. Biol. Med. 204:289-300).

[0158] A desired gene can be introduced intracellularly and incorporated within host precursor cell DNA for expression, by homologous recombination (Koller and Smithies, 1989, Proc. Natl. Acad. Sci. USA 86:8932-8935; Zijlstra et al., 1989, Nature 342:435-438).

[0159] In a specific embodiment, the desired gene recombinantly expressed in the precursor cell to be introduced for purposes of gene therapy comprises an inducible promoter operably linked to the coding region, such that expression of the recombinant gene is controllable by controlling the presence or absence of the appropriate inducer of transcription.

[0160] In another embodiment, if a greater number of differentiated cells is desired before administering to a patient then the precursor cells can be differentiated prior to expansion. In another embodiment, one can expand and differentiate the precursor cells simultaneously such that greater numbers of differentiated cells are obtained.

[0161] 5.7. Pharmaceutical Compositions

[0162] The invention provides methods of treatment by administration to a subject of a pharmaceutical (therapeutic) composition comprising a therapeutically effective amount of a recombinant or non-recombinant cell, preferably a stem or progenitor cell. Such a stem cell or recombinant stem cell envisioned for therapeutic use is referred to hereinafter as a “Therapeutic” or “Therapeutic of the invention.” In a preferred aspect, the Therapeutic is substantially purified. The subject is preferably an animal, including but not limited to animals such as cows, pigs, horses, chickens, cats, dogs, etc., and is preferably a mammal, and most preferably human.

[0163] The present invention provides pharmaceutical compositions. Such compositions comprise a therapeutically effective amount of a Therapeutic, and a pharmaceutically acceptable carrier or excipient. Such a carrier includes but is not limited to saline, buffered saline, dextrose, water, glycerol, ethanol, and combinations thereof. The carrier and composition can be sterile. The formulation should suit the mode of administration.

[0164] The composition, if desired, can also contain minor amounts of wetting or emulsifying agents, or pH buffering agents. The composition can be a liquid solution, suspension, or emulsion.

[0165] In a preferred embodiment, the composition is formulated in accordance with routine procedures as a pharmaceutical composition adapted for intravenous administration to human beings. Typically, compositions for intravenous administration are solutions in sterile isotonic aqueous buffer. Where necessary, the composition may also include a solubilizing agent and a local anesthetic such as lignocaine to ease pain at the site of the injection.

[0166] 5.8. Transplantation

[0167] The expanded stem cell populations of the present invention whether recombinantly expressing a desired gene or not can be transplanted into a patient for the treatment of disease or injury or for gene therapy by any method known in the art which is appropriate for the type of stem cells being transplanted and the transplant site. Hematopoietic stem cells can be transplanted intravenously, as can liver stem cells which will locate to the liver. Neural stem cells can be transplanted directly into the brain at the site of injury or disease.

[0168] Methods of introduction include but are not limited to intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous, intranasal, and epidural routes. The compounds may be administered by any convenient route, for example by infusion or bolus injection, by absorption through epithelial or mucocutaneous linings (e.g., oral mucosa, rectal and intestinal mucosa, etc.) and may be administered together with other biologically active agents. Administration can be systemic or local. In addition, it may be desirable to introduce the pharmaceutical compositions of the invention into the central nervous system by any suitable route, including intraventricular and intrathecal injection; intraventricular injection may be facilitated by an intraventricular catheter, for example, attached to a reservoir, such as an Ommaya reservoir.

[0169] In a specific embodiment, it may be desirable to administer the Therapeutics of the invention locally to the area in need of treatment; this may be achieved by, for example, and not by way of limitation, local infusion during surgery, topical application, e.g., in conjunction with a wound dressing after surgery, by injection, by means of a catheter, or by means of an implant, said implant being of a porous, non-porous, or gelatinous material, including membranes, such as sialastic membranes, or fibers.

[0170] The following describes exemplary methods which can be modified for the transplantation of precursor cells: Protocols for the isolation and transplantation of fetal tissues in humans have been reported and clinical trials involving these studies having been carried out. For example, Lindvall et al., 1990, Science 247:574-577, have described results regarding grafts and survival of fetal dopamine neurons after transplantation into brain. Rinsing and partial dissociation of precursor cells, if necessary, can be carried out by a modification of that described in Lindvall et al., 1989, Arch. Neurol. 46:615.

[0171] By way of example, implantation of cells into the brain can be performed as follows. Implantation is done at three sites in the left putamen with a stereotactic technique (Lindvall et al., 1989, Arch. Neurol. 46:615). For each site, 20 μl of the dissociated cells is drawn into the instrument (outer diameter, 1.0 mm). The cells are injected along a 10, 12 and 14 mm linear tract, respectively, in either 2.5 μl portions for 15 to 20 seconds each. Between each injection there is a 2 minute delay, and the cannula is then retracted 1.5 to 1.7 mm. After the final injection, the cannula is left in situ for 8 minutes before being slowly withdrawn from the brain. After surgery the cell viability is assessed following the procedure of Brundin et al., 1985, Brain. Res. 331:251.

[0172] Another example is outlined by Caplan et al., 1993, U.S. Pat. No. 5,226,914. Briefly, after marrow cells are harvested from bone marrow plugs and the marrow mesenchymal, stem cells are separated by centrifugation. The stem cells are isolated further by selective adherence to the plastic or glass surface of a tissue culture dish. The stem cells are allowed to proliferate but not differentiate. Porous ceramic cubes composed of 60% hydroxyapatite and 40% β-tricalcium phosphate are added to the cells under a slight vacuum. The cubes with adhered cells are implanted into incisional pockets along the backs of nude mice. The mesenchymal stem cells differentiate into bone.

[0173] The titer of stem cells transplanted or the amount of the Therapeutic of the invention which will be effective in the treatment of a particular disorder or condition will depend on the nature of the disorder or condition, and can be determined by standard clinical techniques. In addition, in vitro assays may optionally be employed to help identify optimal dosage ranges. The precise dose to be employed in the formulation will also depend on the route of administration, and the seriousness of the disease or disorder, and should be decided according to the judgment of the practitioner and each patient's circumstances.

[0174] 6. Inhibition of Ras-1-Mediated Signaling by Activated Notch in Drosophila Eye

[0175] In the cone cell precursors of the developing Drosophila eye, Notch activation and Ras1-mediated signaling separately cause opposite cell-fate alterations. Co-expression studies in these cells demonstrate that Notch activation inhibits the neural differentiation produced by constitutively activated components of a well-defined inductive signaling cascade, including the Sevenless receptor tyrosine kinase, Ras1 and Raf.

[0176] The sevenless signaling pathway is required only for the induction of the R7 photoreceptor cell by the previously determined R8 cell of each ommatidium. The interaction of the sevenless gene product and its ligand, encoded by the bride of sevenless (boss) gene, normally occurs only between two particular cell types during a narrow developmental time window (Basler and Hafen, 1989, Development 107:723-731; Mullins and Rubin, 1991, Proc. Natl. Acad. Sci. USA 88:9387-9391; Kramer et al., 1991, Nature 352:207-212). Plies mutant for either or both genes display a very specific phenotype: misrouting of the R7 cell precursor into the cone-cell fate (Tomlinson and Ready, 1986, Science 231:400-402, 1987, Dev. Biol. 123:264-275; Reinke and Zipursky, 1988, Cell 55:321-330). Within each ommatidium, sevenless is expressed in a small set of cells separated by no more than a few cell diameters, consisting of the R3, R4, and R7 precursor cells, the four cone cell precursor cells, and up to two so-called ‘mystery cells’ (Tomlinson et al., 1987, Cell 51:143-150; Bowtell et al., 1989, Proc. Natl. Acad. Sci. USA 86:6245-6249; Basler et al., 1989, EMBO J. 8:2381-2386). In wild-type flies, only the R7 precursor cell ever comes into contact with the R8 cell, which is the only eye disc cell type that expresses bride of sevenless, resulting in the recruitment of one R7 cell per ommatidium (Kramer et al., 1991, Nature 352:207-212). Experiments in which sev and boss were expressed ubiquitously under heat-shock gene control have demonstrated that the spatially restricted presentation of ligand by the R8 cell is a crucial feature of this inductive signalling mechanism (Basler and Hafen, 1989, Science 243:931-934; Bowtell et al., 1989, Cell 56:931-936; Van Vactor et al., 1991, Cell 67:1145-1155). Recent studies have shown that activation of the Sevenless receptor tyrosine kinase initiates a signaling cascade involving the activation of Ras1 and the subsequent activation of Raf (Simon et al., 1991, Cell 67:701-716; Bonfini et al., 1992, Science 255:603-606; Dickson et al., 1992, Genes Dev. 6:2327-2339; Dickson et al., Nature 360:600-603). Ras1 and Raf are also downstream targets of other receptor tyrosine kinases in Drosophila, including the torso kinase and the Drosophila EGF receptor homolog (Ambrosio et al., 1989, Nature 342:288-291; Simon et al., 1991, Cell 67:701-716; Doyle and Bishop, 1993, Genes Dev. 7:633-646; Melnick et al., 1993, Development 118:127-138; Diaz-Benjumea and Hafen, 1994, Development 120:569-578).

[0177] In contrast to sevenless-mediated signalling, the signalling mechanism involving Notch appears to regulate a common step in cell-fate commitment throughout development. The Drosophila Notch gene encodes a large transmembrane receptor protein with an extracellular domain consisting of 36 tandem EGF-like repeats and 3 Notch/lin-12 repeats as well as an intracellular domain containing 6 tandem cdc10/ankyrin repeats (Wharton et al., 1985, Cell 43:567-581; Kidd et al., 1986, Mol. Cell. Biol. 6:3094-3108). Unlike the sev and boss gene products, the Drosophila Notch protein is widely expressed in developing tissues, including all or most cells of the imaginal eye disc (Johansen et al., 1989, J. Cell Biol. 109:2427-2440; Kidd et al., 1989, Genes Dev. 3:1113-1129; Fehon et al., 1991, J. Cell. Biol. 113:657-669). Analysis of Notch gene mutant phenotypes has revealed that Notch function is required for numerous developmental processes, including embryonic neurogenesis (Poulson, 1937, Proc. Natl. Acad. Sci. USA 23:133-137, 1940, J. Exp. Zool. 83:271-325), mesoderm differentiation (Corbin et al., 1991, Cell 67:311-323), axonal pathfinding (Giniger et al., 1993, Development 117:431-440), oogenesis (Ruohola et al., 1991, Cell 66:433-449; Xu et al., 1992, Development 115:913-922; Cummings and Cronmiller, 1994, Development 120:381-394), and differentiation of adult peripheral nervous system structures (Cagan and Ready, 1989, Genes Dev. 3:1099-1112; Palka et al., 1990, Development 109:167-175; Hartenstein and Posakony, 1990, Dev. Biol. 142:13-30; Hartenstein et al., 1992, Development 116:1203-1220). A detailed study of the phenotypic effects of the conditional loss-of-function allele Notch^(tsl) has shown that every cell type of the adult eye, including the R7 cell, requires Notch activity at some stage for its proper cell-fate specification (Cagan and Ready, 1989, Genes Dev. 3:1099-1112).

[0178] In the absence of boss gene function, the sevenless-expressing cells of each ommatidium may be induced to differentiate as neurons by ectopic activation of the Sevenless protein, Ras1, or Raf (Basler et al., 1991, Cell 64:1069-1081; Fortini et al., 1992, Nature 355:559-561; Dickson et al., 1992, Genes Dev. 6:2327-2339; Dickson et al., Nature 360:600-603). Evidence is presented below that the neural induction of these cells by activated sevenless pathway components is blocked by constitutive Notch activation in the developing eye imaginal disc. These results indicate that the signal mediated by Notch and its ligands are integrated with the cell type-specific inductive signal mediated by Sevenless at a point downstream of Raf during R7 photoreceptor cell fate specification. Since both Ras1 and Raf are utilized by other tissue-specific inductive signalling pathways, our data implies that Notch may exert regulatory effects on these pathways as well.

[0179] 6.1. Materials and Methods

[0180] Drosophila Culture:

[0181] Flies were grown on standard medium at 18° C. for optimal imaginal disc growth.

[0182] Immunohistochemistry:

[0183] Antibody staining of eye imaginal discs was performed as described in Gaul et al., 1992, Cell 68:1007-1019. For the Notch/ELAV stainings, mouse mAb C17.9C6 (Fehon et al., 1990, Cell 61:523-534) and rat mAb 7E8A10 (Robinow and White, 1991, J. Neurobiol. 22:443-461) were used at 1:2000 and 1:1 dilutions, respectively. For the Notch/Sevenless double stainings, rat polyclonal Ab Rat5 (R. G. Fehon, I. Rebay, and S. Artavanis-Tsakonas, unpublished) and mouse mAb sev150C3 (Banerjee et al., 1987, Cell 51:151-158) were used at 1:500 and 1:1000 dilutions, respectively. In both cases, goat anti-mouse FITC-conjugated and goat anti-rat Texas Red-conjugated double-label grade secondary antibodies (Jackson ImmunoResearch Laboratories, Inc.) were used at 1:250 and 1:500 dilutions, respectively.

[0184] Confocal Microscopy:

[0185] Confocal microscopy and image processing were performed as described by Xu et al., 1992, Development 115:913-922.

6.2. Results

[0186] Previous studies on R7 photoreceptor cell determination in Drosophila have shown that specification of neural fate in the R7 precursor cell is initiated by ligand-induced activation of the receptor tyrosine kinase encoded by sevenless (reviewed in Greenwald and Rubin, 1992, Cell 68:271-281), which is expressed strongly in a subset of uncommitted cells in each developing ommatidium, namely the R3, R4, and R7 precursor cells, the four cone cell precursors, and up to two so-called ‘mystery cells’ (Tomlinson et al., 1987, Cell 51:143-150; Bowtell et al., 1989, Proc. Natl. Acad. Sci. USA 86:6245-6249; Basler et al., 1989, EMBO J. 8:2381-2386). Activation of the Sevenless tyrosine kinase results in the subsequent activation of Ras1 (Simon et al., 1991, Cell 67:701-716; Bonfini et al., 1992, Science 255:603-606), which in turn activates Raf (Dickson et al., 1992, Nature 360:600-603). These studies have also led to the production of transgenic fly lines bearing constitutively activated Sevenless, Ras1, and Raf proteins, all expressed under sevenless gene control in the above mentioned cells (Basler et al., 1991, Cell 64:1069-1081; Fortini et al., 1992, Nature 355:559-561; Dickson et al., 1992, Genes Dev. 6:2327-2339; Dickson et al., Nature 360:600-603). In each case, expression of the activated sevenless pathway component drives sevenless-expressing cells into neural fates, as judged by the expression of neural-specific antigens such as BP-104 (Hortsch et al., 1990, Neuron 4:697-709) or ELAV (Bier et al., 1988, Science 240:913-916; Robinow and White, 1991, J. Neurobiol. 22:443-461) in the eye disc. While the wild-type Notch gene is expressed in and required for normal development of all or most eye disc cells (Cagan and Ready, 1989, Genes Dev. 3:1099-1112; Fehon et al., 1991, J. Cell. Biol. 113:657-669), a constitutively activated Notch receptor lacking the extracellular and transmembrane domains expressed under sevenless gene control blocks cell-fate commitment, preventing ELAV expression in neural precursors and causing cell-fate misspecifications among the sevenless-expressing cells (Fortini et al., 1993, Nature 365:555-557).

[0187] To determine whether the block imposed by activated Notch upon neural differentiation can be circumvented by constitutive activation of any of the sevenless signalling pathway components, transgenic flies were produced co-expressing activated Notch and activated sevenless pathway factors in the sevenless-expressing cells. Eye discs of these flies were double-stained with antibodies directed against Notch and against the ELAV protein to determine whether cells expressing activated Notch are capable of neural induction by activated Sevenless, activated Ras, or activated Raf. Since ELAV is a nuclear antigen, we chose to use an activated Notch construct, termed sev-Notch^(nucl), that produces nuclear Notch protein localization (Fortini et al., 1993, Nature 365:555-557). This nuclear Notch expression is easily distinguished from the apical membrane distribution of the endogenous wild-type Notch protein (Fehon et al., 1991, J. Cell. Biol. 113:657-669; Fortini et al., 1993, Nature 365:555-557). Nuclear translocation of the Notch protein apparently is not required for its activated behavior, since the same phenotypic effects are caused by a truncated Notch protein lacking extracellular but not transmembrane sequences that is apically localized, as judged by antibody staining experiments (Fortini et al., 1993, Nature 365:555-557).

[0188] The analysis was restricted to the four cone cell precursors of each developing ommatidium for the following reasons. First, the cone cell precursor nuclei are easily identified by their distinctive sausage-shaped morphology. Second, the cone cell precursors are normally non-neural and thus should only be ELAV-positive as a result of the transgene-driven activated sevenless pathway components. Third, Notch expression in sev-Notch^(nucl) cone cell precursor nuclei persists throughout those ommatidial rows of the posterior eye disc in which cone cell precursors exhibit strong ELAV expression if they are transformed into neurons (Fortini et al., 1992, Nature 355:559-561, 1993, Nature 365:555-557; Gaul et al., 1992, Cell. 68:1007-1019; Dickson et al., 1992, Nature 360:600-603). By contrast, the nuclear Notch expression in R3 and R4 precursor cells and mystery cells is more transient, subsiding prior to the onset of ELAV expression (Fortini et al., 1993, Nature 365:555-557).

[0189] Notch-positive cone cell precursor nuclei were scored for ELAV expression in sev-Notchnucl flies also carrying either the activated Sevenless tyrosine kinase construct sev-S11 (Basler et al., 1991, Cell 64:1069-1081), the activated Ras1 construct sevRas1^(Val12) (Fortini et al., 1992, Nature 355:559-561), or the activated Raf construct sE-raf^(torY9) (Dickson et al., 1992, Genes Dev. 6:2327-2339; Dickson et al., Nature 360:600-603). For each genotype, 500 Notch-positive cone cell precursor nuclei in ommatidial rows 15-25 were examined, representing at least six separate pairs of eye discs. In no case did we observe any cone cell precursor nuclei positive for both Notch and ELAV antigens (FIG. 5). We frequently found that not all four cone cell precursor nuclei in an ommatidium express Notch, and that those which do not are often ELAV-positive (FIG. 5). These nuclei presumably correspond to cone cell precursors that do not express sev-Notch^(nucl) efficiently but do express sufficient amounts of an activated sevenless pathway molecule to induce neural differentiation. Identical results were obtained with different sev-Notch^(nucl), sev-S11, and sevRas1^(Val12) transgenic lines as well as with an alternative activated Raf construct sE-raf^(tor4021) (Dickson et al., 1992, Genes Dev. 6:2327-2339; Dickson et al., Nature 360:600-603).

[0190] To rule out the possibility that our failure to detect co-expression of activated Notch and ELAV antigens in cone cell precursor nuclei is due to some mechanism that prevents two different sevenless promoter constructs from being expressed in the same cell, we double-stained eye discs of transgenic flies bearing both sev-Notchnucl and sev-S11 in a sevenless^(d2) genetic background with antibodies against Notch and against the intracellular 60-kD subunit of Sevenless (Banerjee et al., 1987, Cell 51:151-158). Since sevenless^(d2) flies do not express this subunit (Banerjee et al, 1987), the only Sevenless immunoreactivity detected corresponds to the extracellularly truncated protein produced by the sev-S11 transgene (Basler et al., 1991, Cell 64:1069-1081). It was found that most cone cell precursors showing strong nuclear expression of activated Notch also display strong apical membrane expression of activated Sevenless, demonstrating that both transgenes are coexpressed in these cells (FIG. 6).

6.3. Discussion

[0191] The class of transmembrane receptor proteins encoded by the Notch locus and related genes appears to regulate a common step in cell-fate selection in organisms ranging from nematodes to humans (reviewed in Greenwald and Rubin, 1992, Cell 68:271-281; Fortini and Artavanis-Tsakonas, 1993, Cell 75:1245-1247). In many different cell types, the signal generated by Notch activation renders cells temporarily unable to respond to developmental cues from neighboring cells (Coffman et al., 1993, Cell 73:659-671; Rebay et al., 1993, Cell 74:319-329; Struhl et al., 1993, Cell 74:331-345; Fortini et al., 1993, Nature 365:555-557; Lieber et al., 1993, Genes Dev. 7:1949-1965). The Notch protein and its ligands Delta and Serrate may thus be part of a general mechanism that limits the competence of undifferentiated cells to undergo cell-fate commitment (Coffman et al., 1993, Cell 73:659-671; Fortini and Artavanis-Tsakonas, 1993, Cell 75:1245-1247). This mechanism may play a crucial role in the timing of inductive events by allowing an uncommitted cell to ignore irrelevant signals from adjacent cells until it is presented with the appropriate inductive signal, presumably preceded or accompanied by a signal that inactivates Notch in the recipient cell. Consistent with this notion, genetic analyses in Caenorhabditis and Drosophila have revealed an interdependence between Notch-mediated signaling and several distinct cell type-specific inductive signaling events (reviewed in Horvitz and Sternberg, 1991, Nature 351:535-541; Artavanis-Tsakonas and Simpson, 1991, Trends Genet. 7:403-408; Greenwald and Rubin, 1992, Cell 68:271-281), although little is known about how the different signals are integrated at the molecular level. We have sought to address this question by performing epistasis tests between a constitutively activated Notch receptor and various activated components of the inductive signalling pathway involving the Sevenless receptor tyrosine kinase, Ras1 and Raf in the developing Drosophila eye.

[0192] The results presented here indicate that the Notch receptor protein, in its active state, interferes with the intracellular signal generated by constitutively activated versions of Sevenless, Ras1, and Raf (FIG. 7). Our epistasis data are difficult to reconcile with models in which the Notch protein mediates cell signaling primarily by promoting cell adhesion (Hoppe and Greenspan, 1986, Cell 46:773-783; Greenspan, 1990, New Biologist 2:595-600) or by recruiting cell type-specific receptors and their ligands to specialized membrane regions of polarized epithelia (Singer, 1992, Science 255:1671-1677). Instead, Notch apparently mediates a separate signalling pathway whose input is integrated with that of the Ras1 pathway at some point downstream of Raf, at least in this case. Ras1 and Raf, unlike the sevenless receptor tyrosine kinase, act in many different tissues throughout Drosophila development, as does Notch. For example, genetic studies have identified both Ras1 and Raf as essential components of the signaling pathways initiated by the torso and Drosophila EGF receptor (DER) tyrosine kinases (Ambrosio et al., 1989, Nature 342:288-291; Simon et al., 1991, Cell 67:701-716; Doyle and Bishop, 1993, Genes Dev. 7:633-646; Melnick et al., 1993, Development 118:127-138; Diaz-Benjumea and Hafen, 1994, Development 120:569-578). Moreover, cell-fate specifications involving other types of signalling molecules, such as the Drosophila scabrous, wingless and daughterless gene products, also depend upon Notch gene function (Baker et al., 1990, Science 250:1370-1377; Hing et al., 1994, Mech. Dev., in press; Cummings and Cronmiller, 1994, Development 120:381-394). Thus, the activity state of Notch is likely to play an important regulatory role in modulating signalling by Ras1, Raf, and other signalling molecules in a variety of developmental processes.

[0193] The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and accompanying figures. Such modifications are intended to fall within the scope of the appended claims.

[0194] Various publications are cited herein, the disclosures of which are incorporated by reference in their entireties.

1 4 1 1015 PRT Homo sapiens 1 Ser Asn Pro Cys Gln His Gly Ala Thr Cys Ser Asp Phe Ile Gly Gly 1 5 10 15 Tyr Arg Cys Glu Cys Val Pro Gly Tyr Gln Gly Val Asn Cys Glu Tyr 20 25 30 Glu Val Asp Glu Cys Gln Asn Gln Pro Cys Gln Asn Gly Gly Thr Cys 35 40 45 Ile Asp Leu Val Asn His Phe Lys Cys Ser Cys Pro Pro Gly Thr Arg 50 55 60 Gly Leu Leu Cys Glu Glu Asn Ile Asp Asp Cys Ala Arg Gly Pro His 65 70 75 80 Cys Leu Asn Gly Gly Gln Cys Met Asp Arg Ile Gly Gly Tyr Ser Cys 85 90 95 Arg Cys Leu Pro Gly Phe Ala Gly Glu Arg Cys Glu Gly Asp Ile Asn 100 105 110 Glu Cys Leu Ser Asn Pro Cys Ser Ser Glu Gly Ser Leu Asp Cys Ile 115 120 125 Gln Leu Thr Asn Asp Tyr Leu Cys Val Cys Arg Ser Ala Phe Thr Gly 130 135 140 Arg His Cys Glu Thr Phe Val Asp Val Cys Pro Gln Met Pro Cys Leu 145 150 155 160 Asn Gly Gly Thr Cys Ala Val Ala Ser Asn Met Pro Asp Gly Phe Ile 165 170 175 Cys Arg Cys Pro Pro Gly Phe Ser Gly Ala Arg Cys Gln Ser Ser Cys 180 185 190 Gly Gln Val Lys Cys Arg Lys Gly Glu Gln Cys Val His Thr Ala Ser 195 200 205 Gly Pro Arg Cys Phe Cys Pro Ser Pro Arg Asp Cys Glu Ser Gly Cys 210 215 220 Ala Ser Ser Pro Cys Gln His Gly Gly Ser Cys His Pro Gln Arg Gln 225 230 235 240 Pro Pro Tyr Tyr Ser Cys Gln Cys Ala Pro Pro Phe Ser Gly Ser Arg 245 250 255 Cys Glu Leu Tyr Thr Ala Pro Pro Ser Thr Pro Pro Ala Thr Cys Leu 260 265 270 Ser Gln Tyr Cys Ala Asp Lys Ala Arg Asp Gly Val Cys Asp Glu Ala 275 280 285 Cys Asn Ser His Ala Cys Gln Trp Asp Gly Gly Asp Cys Ser Leu Thr 290 295 300 Met Glu Asn Pro Trp Ala Asn Cys Ser Ser Pro Leu Pro Cys Trp Asp 305 310 315 320 Tyr Ile Asn Asn Gln Cys Asp Glu Leu Cys Asn Thr Val Glu Cys Leu 325 330 335 Phe Asp Asn Phe Glu Cys Gln Gly Asn Ser Lys Thr Cys Lys Tyr Asp 340 345 350 Lys Tyr Cys Ala Asp His Phe Lys Asp Asn His Cys Asn Gln Gly Cys 355 360 365 Asn Ser Glu Glu Cys Gly Trp Asp Gly Leu Asp Cys Ala Ala Asp Gln 370 375 380 Pro Glu Asn Leu Ala Glu Gly Thr Leu Val Ile Val Val Leu Met Pro 385 390 395 400 Pro Glu Gln Leu Leu Gln Asp Ala Arg Ser Phe Leu Arg Ala Leu Gly 405 410 415 Thr Leu Leu His Thr Asn Leu Arg Ile Lys Arg Asp Ser Gln Gly Glu 420 425 430 Leu Met Val Tyr Pro Tyr Tyr Gly Glu Lys Ser Ala Ala Met Lys Lys 435 440 445 Gln Arg Met Thr Arg Arg Ser Leu Pro Gly Glu Gln Glu Gln Glu Val 450 455 460 Ala Gly Ser Lys Val Phe Leu Glu Ile Asp Asn Arg Gln Cys Val Gln 465 470 475 480 Asp Ser Asp His Cys Phe Lys Asn Thr Asp Ala Ala Ala Ala Leu Leu 485 490 495 Ala Ser His Ala Ile Gln Gly Thr Leu Ser Tyr Pro Leu Val Ser Val 500 505 510 Val Ser Glu Ser Leu Thr Pro Glu Arg Thr Gln Leu Leu Tyr Leu Leu 515 520 525 Ala Val Ala Val Val Ile Ile Leu Phe Ile Ile Leu Leu Gly Val Ile 530 535 540 Met Ala Lys Arg Lys Arg Lys His Gly Ser Leu Trp Leu Pro Glu Gly 545 550 555 560 Phe Thr Leu Arg Arg Asp Ala Ser Asn His Lys Arg Arg Glu Pro Val 565 570 575 Gly Gln Asp Ala Val Gly Leu Lys Asn Leu Ser Val Gln Val Ser Glu 580 585 590 Ala Asn Leu Ile Gly Thr Gly Thr Ser Glu His Trp Val Asp Asp Glu 595 600 605 Gly Pro Gln Pro Lys Lys Val Lys Ala Glu Asp Glu Ala Leu Leu Ser 610 615 620 Glu Glu Asp Asp Pro Ile Asp Arg Arg Pro Trp Thr Gln Gln His Leu 625 630 635 640 Glu Ala Ala Asp Ile Arg Arg Thr Pro Ser Leu Ala Leu Thr Pro Pro 645 650 655 Gln Ala Glu Gln Glu Val Asp Val Leu Asp Val Asn Val Arg Gly Pro 660 665 670 Asp Gly Cys Thr Pro Leu Met Leu Ala Ser Leu Arg Gly Gly Ser Ser 675 680 685 Asp Leu Ser Asp Glu Asp Glu Asp Ala Glu Asp Ser Ser Ala Asn Ile 690 695 700 Ile Thr Asp Leu Val Tyr Gln Gly Ala Ser Leu Gln Ala Gln Thr Asp 705 710 715 720 Arg Thr Gly Glu Met Ala Leu His Leu Ala Ala Arg Tyr Ser Arg Ala 725 730 735 Asp Ala Ala Lys Arg Leu Leu Asp Ala Gly Ala Asp Ala Asn Ala Gln 740 745 750 Asp Asn Met Gly Arg Cys Pro Leu His Ala Ala Val Ala Ala Asp Ala 755 760 765 Gln Gly Val Phe Gln Ile Leu Ile Arg Asn Arg Val Thr Asp Leu Asp 770 775 780 Ala Arg Met Asn Asp Gly Thr Thr Pro Leu Ile Leu Ala Ala Arg Leu 785 790 795 800 Ala Val Glu Gly Met Val Ala Glu Leu Ile Asn Cys Gln Ala Asp Val 805 810 815 Asn Ala Val Asp Asp His Gly Lys Ser Ala Leu His Trp Ala Ala Ala 820 825 830 Val Asn Asn Val Glu Ala Thr Leu Leu Leu Leu Lys Asn Gly Ala Asn 835 840 845 Arg Asp Met Gln Asp Asn Lys Glu Glu Thr Pro Leu Phe Leu Ala Ala 850 855 860 Arg Glu Gly Ser Tyr Glu Ala Ala Lys Ile Leu Leu Asp His Phe Ala 865 870 875 880 Asn Arg Asp Ile Thr Asp His Met Asp Arg Leu Pro Arg Asp Val Ala 885 890 895 Arg Asp Arg Met His His Asp Ile Val Arg Leu Leu Asp Glu Tyr Asn 900 905 910 Val Thr Pro Ser Pro Pro Gly Thr Val Leu Thr Ser Ala Leu Ser Pro 915 920 925 Val Ile Cys Gly Pro Asn Arg Ser Phe Leu Ser Leu Lys His Thr Pro 930 935 940 Met Gly Lys Lys Ser Arg Arg Pro Ser Ala Lys Ser Thr Met Pro Thr 945 950 955 960 Ser Leu Pro Asn Leu Ala Lys Glu Ala Lys Asp Ala Lys Gly Ser Arg 965 970 975 Arg Lys Lys Ser Leu Ser Glu Lys Val Gln Leu Ser Glu Ser Ser Val 980 985 990 Thr Leu Ser Pro Val Asp Ser Leu Glu Ser Pro His Thr Tyr Val Ser 995 1000 1005 Asp Thr Thr Ser Ser Pro Met 1010 1015 2 1068 PRT Homo sapiens misc_feature (612)..(612) Xaa can be any naturally occurring amino acid 2 Pro Ser Pro Cys Gln Asn Gly Ala Thr Cys Thr Asp Tyr Leu Gly Gly 1 5 10 15 Tyr Ser Cys Lys Cys Val Ala Gly Tyr His Gly Val Asn Cys Ser Glu 20 25 30 Glu Ile Asp Glu Cys Leu Ser His Pro Cys Gln Asn Gly Gly Thr Cys 35 40 45 Leu Asp Leu Pro Asn Thr Tyr Lys Cys Ser Cys Pro Trp Gly Thr Gln 50 55 60 Gly Val His Cys Glu Ile Asn Val Asp Asp Cys Asn Pro Pro Val Asp 65 70 75 80 Pro Val Ser Trp Ser Pro Lys Cys Phe Asn Asn Gly Thr Cys Val Asp 85 90 95 Gln Val Gly Gly Tyr Ser Cys Thr Cys Pro Pro Gly Phe Val Gly Glu 100 105 110 Arg Cys Glu Gly Asp Val Asn Glu Cys Leu Ser Asn Pro Cys Asp Ala 115 120 125 Arg Gly Thr Gln Asn Cys Val Gln Arg Val Asn Asp Phe His Cys Glu 130 135 140 Cys Arg Ala Gly His Thr Gly Arg Arg Cys Glu Ser Val Ile Asn Gly 145 150 155 160 Cys Lys Gly Lys Pro Cys Lys Asn Gly Gly Thr Cys Ala Val Ala Ser 165 170 175 Asn Thr Ala Arg Gly Phe Ile Cys Lys Cys Pro Ala Gly Phe Glu Gly 180 185 190 Ala Thr Cys Glu Asn Asp Ala Arg Thr Cys Gly Ser Leu Arg Cys Leu 195 200 205 Asn Gly Gly Thr Cys Ile Ser Gly Pro Arg Ser Pro Thr Cys Leu Cys 210 215 220 Leu Gly Pro Phe Thr Gly Pro Glu Cys Gln Phe Pro Ala Ser Ser Pro 225 230 235 240 Cys Leu Gly Gly Asn Pro Cys Tyr Asn Gln Gly Thr Cys Glu Pro Thr 245 250 255 Ser Glu Ser Pro Phe Tyr Arg Cys Leu Cys Pro Ala Lys Phe Asn Gly 260 265 270 Leu Leu Cys His Ile Leu Asp Tyr Ser Phe Gly Gly Gly Ala Gly Arg 275 280 285 Asp Ile Pro Pro Pro Leu Ile Glu Glu Ala Cys Glu Leu Pro Glu Cys 290 295 300 Gln Glu Asp Ala Gly Asn Lys Val Cys Ser Leu Gln Cys Asn Asn His 305 310 315 320 Ala Cys Gly Trp Asp Gly Gly Asp Cys Ser Leu Asn Phe Asn Asp Pro 325 330 335 Trp Lys Asn Cys Thr Gln Ser Leu Gln Cys Trp Lys Tyr Phe Ser Asp 340 345 350 Gly His Cys Asp Ser Gln Cys Asn Ser Ala Gly Cys Leu Phe Asp Gly 355 360 365 Phe Asp Cys Gln Arg Ala Glu Gly Gln Cys Asn Pro Leu Tyr Asp Gln 370 375 380 Tyr Cys Lys Asp His Phe Ser Asp Gly His Cys Asp Gln Gly Cys Asn 385 390 395 400 Ser Ala Glu Cys Glu Trp Asp Gly Leu Asp Cys Ala Glu His Val Pro 405 410 415 Glu Arg Leu Ala Ala Gly Thr Leu Val Val Val Val Leu Met Pro Pro 420 425 430 Glu Gln Leu Arg Asn Ser Ser Phe His Phe Leu Trp Glu Leu Ser Arg 435 440 445 Val Leu His Thr Asn Val Val Phe Lys Arg Asp Ala His Gly Gln Gln 450 455 460 Met Ile Phe Pro Tyr Tyr Gly Arg Glu Glu Glu Leu Arg Lys His Pro 465 470 475 480 Ile Lys Arg Ala Ala Glu Gly Trp Ala Ala Pro Asp Ala Leu Leu Gly 485 490 495 Gln Val Lys Ala Ser Leu Leu Pro Gly Gly Ser Glu Gly Gly Trp Trp 500 505 510 Trp Arg Glu Leu Asp Pro Met Asp Val Arg Gly Ser Ile Val Tyr Leu 515 520 525 Glu Ile Asp Asn Trp Gln Cys Val Gln Ala Ser Ser Gln Cys Phe Gln 530 535 540 Ser Ala Thr Asp Val Ala Ala Phe Leu Gly Ala Leu Ala Ser Leu Gly 545 550 555 560 Ser Leu Asn Ile Pro Tyr Lys Ile Glu Ala Val Gln Ser Glu Thr Val 565 570 575 Glu Pro Pro Pro Pro Ala Gln Leu His Phe Met Tyr Val Ala Ala Ala 580 585 590 Ala Phe Val Leu Leu Phe Phe Val Gly Cys Gly Val Leu Leu Ser Arg 595 600 605 Lys Arg Trp Xaa Gln His Gly Gln Leu Trp Phe Pro Glu Gly Phe Lys 610 615 620 Val Ser Glu Ala Ser Lys Lys Lys Trp Trp Glu Xaa Leu Gly Glu Asp 625 630 635 640 Ser Val Gly Leu Lys Pro Leu Lys Asn Ala Ser Asp Gly Ala Leu Met 645 650 655 Asp Asp Asn Gln Asn Glu Trp Gly Asp Glu Asp Leu Glu Thr Lys Lys 660 665 670 Phe Trp Phe Glu Glu Pro Val Val Leu Pro Asp Leu Asp Asp Gln Thr 675 680 685 Asp His Trp Gln Trp Thr Gln Gln His Leu Asp Ala Ala Asp Leu Arg 690 695 700 Met Ser Ala Met Ala Pro Thr Pro Pro Gln Gly Glu Val Asp Ala Asp 705 710 715 720 Cys Met Asp Val Asn Val Arg Gly Pro Asp Gly Phe Thr Pro Leu Met 725 730 735 Ile Ala Ser Cys Ser Gly Gly Gly Leu Glu Thr Gly Asn Ser Glu Glu 740 745 750 Glu Glu Asp Ala Pro Ala Val Ile Ser Asp Phe Ile Tyr Gln Gly Ala 755 760 765 Ser Leu His Asn Gln Thr Asp Arg Thr Gly Glu Thr Ala Leu His Leu 770 775 780 Ala Ala Arg Tyr Ser Arg Ser Asp Ala Ala Lys Arg Leu Leu Glu Ala 785 790 795 800 Ser Ala Asp Ala Asn Ile Gln Asp Asn Met Gly Arg Thr Pro Leu His 805 810 815 Ala Ala Val Ser Ala Asp Ala Gln Gly Val Phe Gln Ile Leu Ile Trp 820 825 830 Asn Arg Ala Thr Asp Leu Asp Ala Arg Met His Asp Gly Thr Thr Pro 835 840 845 Leu Ile Leu Ala Ala Arg Leu Ala Val Glu Gly Met Leu Glu Asp Leu 850 855 860 Ile Asn Ser His Ala Asp Val Asn Ala Val Asp Asp Leu Gly Lys Ser 865 870 875 880 Ala Leu His Trp Ala Ala Ala Val Asn Asn Val Asp Ala Ala Val Val 885 890 895 Leu Leu Lys Asn Gly Ala Asn Lys Asp Met Gln Asn Asn Arg Glu Glu 900 905 910 Thr Pro Leu Phe Leu Ala Ala Trp Glu Gly Ser Tyr Glu Thr Ala Lys 915 920 925 Val Leu Leu Asp His Phe Ala Asn Trp Asp Ile Thr Asp His Met Asp 930 935 940 Arg Leu Pro Arg Asp Ile Ala Gln Glu Arg Met His His Asp Ile Val 945 950 955 960 Arg Leu Leu Asp Glu Tyr Asn Leu Val Arg Ser Pro Gln Leu His Gly 965 970 975 Ala Pro Leu Gly Gly Thr Pro Thr Leu Ser Pro Pro Leu Cys Ser Pro 980 985 990 Asn Gly Tyr Leu Gly Ser Leu Lys Pro Gly Val Gln Gly Lys Lys Val 995 1000 1005 Arg Lys Pro Ser Ser Lys Gly Leu Ala Cys Gly Ser Lys Glu Ala 1010 1015 1020 Lys Asp Leu Lys Ala Trp Arg Lys Lys Ser Gln Asp Gly Lys Gly 1025 1030 1035 Cys Leu Leu Asp Ser Ser Gly Met Leu Ser Pro Val Asp Ser Leu 1040 1045 1050 Glu Ser Pro His Gly Tyr Leu Ser Asp Val Ala Ser Pro Pro Leu 1055 1060 1065 3 1064 PRT Homo sapiens 3 Pro Asn Pro Cys Gln Asn Gly Ala Thr Cys Thr Asp Tyr Leu Gly Gly 1 5 10 15 Tyr Ser Cys Glu Cys Val Ala Gly Tyr His Gly Val Asn Cys Ser Glu 20 25 30 Glu Ile Asn Glu Cys Leu Ser His Pro Cys Gln Asn Gly Gly Thr Cys 35 40 45 Ile Asp Leu Ile Asn Thr Tyr Lys Cys Ser Cys Pro Arg Gly Thr Gln 50 55 60 Gly Val His Cys Glu Ile Asn Val Asp Asp Cys Thr Pro Phe Tyr Asp 65 70 75 80 Ser Phe Thr Leu Glu Pro Lys Cys Phe Asn Asn Gly Lys Cys Ile Asp 85 90 95 Arg Val Gly Gly Tyr Asn Cys Ile Cys Pro Pro Gly Phe Val Gly Glu 100 105 110 Arg Cys Glu Gly Asp Val Asn Glu Cys Leu Ser Asn Pro Cys Asp Ser 115 120 125 Arg Gly Thr Gln Asn Cys Ile Gln Leu Val Asn Asp Tyr Arg Cys Glu 130 135 140 Cys Arg Gln Gly Phe Thr Gly Arg Arg Cys Glu Ser Val Val Asp Gly 145 150 155 160 Cys Lys Gly Met Pro Cys Arg Asn Gly Gly Thr Cys Ala Val Ala Ser 165 170 175 Asn Thr Glu Arg Gly Phe Ile Cys Lys Cys Pro Pro Gly Phe Asp Gly 180 185 190 Ala Thr Cys Glu Tyr Asp Ser Arg Thr Cys Ser Asn Leu Arg Cys Gln 195 200 205 Asn Gly Gly Thr Cys Ile Ser Val Leu Thr Ser Ser Lys Cys Val Cys 210 215 220 Ser Glu Gly Tyr Thr Gly Ala Thr Cys Gln Tyr Pro Val Ile Ser Pro 225 230 235 240 Cys Ala Ser His Pro Cys Tyr Asn Gly Gly Thr Cys Gln Phe Phe Ala 245 250 255 Glu Glu Pro Phe Phe Gln Cys Phe Cys Pro Lys Asn Phe Asn Gly Leu 260 265 270 Phe Cys His Ile Leu Asp Tyr Glu Phe Pro Gly Gly Leu Gly Lys Asn 275 280 285 Ile Thr Pro Pro Asp Asn Asp Asp Ile Cys Glu Asn Glu Gln Cys Ser 290 295 300 Glu Leu Ala Asp Asn Lys Val Cys Asn Ala Asn Cys Asn Asn His Ala 305 310 315 320 Cys Gly Trp Asp Gly Gly Asp Cys Ser Leu Asn Phe Asn Asp Pro Trp 325 330 335 Lys Asn Cys Thr Gln Ser Leu Gln Cys Trp Lys Tyr Phe Asn Asp Gly 340 345 350 Lys Cys Asp Ser Gln Cys Asn Asn Thr Gly Cys Leu Tyr Asp Gly Phe 355 360 365 Asp Cys Gln Lys Val Glu Val Gln Cys Asn Pro Leu Tyr Asp Gln Tyr 370 375 380 Cys Lys Asp His Phe Gln Asp Gly His Cys Asp Gln Gly Cys Asn Asn 385 390 395 400 Ala Glu Cys Glu Trp Asp Gly Leu Asp Cys Ala Asn Met Pro Glu Asn 405 410 415 Leu Ala Glu Gly Thr Leu Val Leu Val Val Leu Met Pro Pro Glu Arg 420 425 430 Leu Lys Asn Asn Ser Val Asn Phe Leu Arg Glu Leu Ser Arg Val Leu 435 440 445 His Thr Asn Val Val Phe Lys Lys Asp Ser Lys Gly Glu Tyr Lys Ile 450 455 460 Tyr Pro Tyr Tyr Gly Asn Glu Glu Glu Leu Lys Lys His His Ile Lys 465 470 475 480 Arg Ser Thr Asp Tyr Trp Ser Asp Ala Pro Ser Ala Ile Phe Ser Thr 485 490 495 Met Lys Glu Ser Ile Leu Leu Gly Arg His Arg Arg Glu Leu Asp Glu 500 505 510 Met Glu Val Arg Gly Ser Ile Val Tyr Leu Glu Ile Asp Asn Arg Gln 515 520 525 Cys Tyr Lys Ser Ser Ser Gln Cys Phe Asn Ser Ala Thr Asp Val Ala 530 535 540 Ala Phe Leu Gly Ala Leu Ala Ser Leu Gly Ser Leu Asp Thr Leu Ser 545 550 555 560 Tyr Lys Ile Glu Ala Val Lys Ser Glu Asn Met Glu Thr Pro Lys Pro 565 570 575 Ser Thr Leu Tyr Pro Met Leu Ser Met Leu Val Ile Pro Leu Leu Ile 580 585 590 Ile Phe Val Phe Met Met Val Ile Val Asn Lys Lys Arg Arg Arg Glu 595 600 605 His Asp Ser Phe Gly Ser Pro Thr Ala Leu Phe Gln Lys Asn Pro Ala 610 615 620 Lys Arg Asn Gly Glu Thr Pro Trp Glu Asp Ser Val Gly Leu Lys Pro 625 630 635 640 Ile Lys Asn Met Thr Asp Gly Ser Phe Met Asp Asp Asn Gln Asn Glu 645 650 655 Trp Gly Asp Glu Glu Thr Leu Glu Asn Lys Arg Phe Arg Phe Glu Glu 660 665 670 Gln Val Ile Leu Pro Glu Leu Val Asp Asp Lys Thr Asp Pro Arg Gln 675 680 685 Trp Thr Arg Gln His Leu Asp Ala Ala Asp Leu Arg Ile Ser Ser Met 690 695 700 Ala Pro Thr Pro Pro Gln Gly Glu Ile Glu Ala Asp Cys Met Asp Val 705 710 715 720 Asn Val Arg Gly Pro Asp Gly Phe Thr Pro Leu Met Ile Ala Ser Cys 725 730 735 Ser Gly Gly Gly Leu Glu Thr Gly Asn Ser Glu Glu Glu Glu Asp Ala 740 745 750 Ser Ala Asn Met Ile Ser Asp Phe Ile Gly Gln Gly Ala Gln Leu His 755 760 765 Asn Gln Thr Asp Arg Thr Gly Glu Thr Ala Leu His Leu Ala Ala Arg 770 775 780 Tyr Ala Arg Ala Asp Ala Ala Lys Arg Leu Leu Glu Ser Ser Ala Asp 785 790 795 800 Ala Asn Val Gln Asp Asn Met Gly Arg Thr Pro Leu His Ala Ala Val 805 810 815 Ala Ala Asp Ala Gln Gly Val Phe Gln Ile Leu Ile Arg Asn Arg Ala 820 825 830 Thr Asp Leu Asp Ala Arg Met Phe Asp Gly Thr Thr Pro Leu Ile Leu 835 840 845 Ala Ala Arg Leu Ala Val Glu Gly Met Val Glu Glu Leu Ile Asn Ala 850 855 860 His Ala Asp Val Asn Ala Val Asp Glu Phe Gly Lys Ser Ala Leu His 865 870 875 880 Trp Ala Ala Ala Val Asn Asn Val Asp Ala Ala Ala Val Leu Leu Lys 885 890 895 Asn Ser Ala Asn Lys Asp Met Gln Asn Asn Lys Glu Glu Thr Ser Leu 900 905 910 Phe Leu Ala Ala Arg Glu Gly Ser Tyr Glu Thr Ala Lys Val Leu Leu 915 920 925 Asp His Tyr Ala Asn Arg Asp Ile Thr Asp His Met Asp Arg Leu Pro 930 935 940 Arg Asp Ile Ala Gln Glu Arg Met His His Asp Ile Val His Leu Leu 945 950 955 960 Asp Glu Tyr Asn Leu Val Lys Ser Pro Thr Leu His Asn Gly Pro Leu 965 970 975 Gly Ala Thr Thr Leu Ser Pro Pro Ile Cys Ser Pro Asn Gly Tyr Met 980 985 990 Gly Asn Met Lys Pro Ser Val Gln Ser Lys Lys Ala Arg Lys Pro Ser 995 1000 1005 Ile Lys Gly Asn Gly Cys Lys Glu Ala Lys Glu Leu Lys Ala Arg 1010 1015 1020 Arg Lys Lys Ser Gln Asp Gly Lys Thr Thr Leu Leu Asp Ser Gly 1025 1030 1035 Ser Ser Gly Val Leu Ser Pro Val Asp Ser Leu Glu Ser Thr His 1040 1045 1050 Gly Tyr Leu Ser Asp Val Ser Ser Pro Pro Leu 1055 1060 4 1139 PRT Homo sapiens 4 Ser Gln Pro Cys Gln Asn Gly Gly Thr Cys Arg Asp Leu Ile Gly Ala 1 5 10 15 Tyr Glu Cys Gln Cys Arg Gln Gly Phe Gln Gly Gln Asn Cys Glu Leu 20 25 30 Asn Ile Asp Asp Cys Ala Pro Asn Pro Cys Gln Asn Gly Gly Thr Cys 35 40 45 His Asp Arg Val Met Asn Phe Ser Cys Ser Cys Pro Pro Gly Thr Met 50 55 60 Gly Ile Ile Cys Glu Ile Asn Lys Asp Asp Cys Lys Pro Gly Ala Cys 65 70 75 80 His Asn Asn Gly Ser Cys Ile Asp Arg Val Gly Gly Phe Glu Cys Val 85 90 95 Cys Gln Pro Gly Phe Val Gly Ala Arg Cys Glu Gly Asp Ile Asn Glu 100 105 110 Cys Leu Ser Asn Pro Cys Ser Asn Ala Gly Thr Leu Asp Cys Val Gln 115 120 125 Leu Val Asn Asn Tyr His Cys Asn Cys Arg Pro Gly His Met Gly Arg 130 135 140 His Cys Glu His Lys Val Asp Phe Cys Ala Gln Ser Pro Cys Gln Asn 145 150 155 160 Gly Gly Asn Cys Asn Ile Arg Gln Ser Gly His His Cys Ile Cys Asn 165 170 175 Asn Gly Phe Tyr Gly Lys Asn Cys Glu Leu Ser Gly Gln Asp Cys Asp 180 185 190 Ser Asn Pro Cys Arg Val Gly Asn Cys Val Val Ala Asp Glu Gly Phe 195 200 205 Gly Tyr Arg Cys Glu Cys Pro Arg Gly Thr Leu Gly Glu His Cys Glu 210 215 220 Ile Asp Thr Leu Asp Glu Cys Ser Pro Asn Pro Cys Ala Gln Gly Ala 225 230 235 240 Ala Cys Glu Asp Leu Leu Gly Asp Tyr Glu Cys Leu Cys Pro Ser Lys 245 250 255 Trp Lys Gly Lys Arg Cys Asp Ile Tyr Asp Ala Asn Tyr Pro Gly Trp 260 265 270 Asn Gly Gly Ser Gly Ser Gly Asn Asp Arg Tyr Ala Ala Asp Leu Glu 275 280 285 Gln Gln Arg Ala Met Cys Asp Lys Arg Gly Cys Thr Glu Lys Gln Gly 290 295 300 Asn Gly Ile Cys Asp Ser Asp Cys Asn Thr Tyr Ala Cys Asn Phe Asp 305 310 315 320 Gly Asn Asp Cys Ser Leu Gly Ile Asn Pro Trp Ala Asn Cys Thr Ala 325 330 335 Asn Glu Cys Trp Asn Lys Phe Lys Asn Gly Lys Cys Asn Glu Glu Cys 340 345 350 Asn Asn Ala Ala Cys His Tyr Asp Gly His Asp Cys Glu Arg Lys Leu 355 360 365 Lys Ser Cys Asp Thr Leu Phe Asp Ala Tyr Cys Gln Lys His Tyr Gly 370 375 380 Asp Gly Phe Cys Asp Tyr Gly Cys Asn Asn Ala Glu Cys Ser Trp Asp 385 390 395 400 Gly Leu Asp Cys Glu Asn Lys Thr Gln Ser Pro Val Leu Ala Glu Gly 405 410 415 Ala Met Ser Val Val Met Leu Met Asn Val Glu Ala Phe Arg Glu Ile 420 425 430 Gln Ala Gln Phe Leu Arg Asn Met Ser His Met Leu Arg Thr Thr Val 435 440 445 Arg Leu Lys Lys Asp Ala Leu Gly His Asp Ile Ile Ile Asn Trp Lys 450 455 460 Asp Asn Val Arg Val Pro Glu Ile Glu Asp Thr Asp Phe Ala Arg Lys 465 470 475 480 Asn Lys Ile Leu Tyr Thr Gln Gln Val His Gln Thr Gly Ile Gln Ile 485 490 495 Tyr Leu Glu Ile Asp Asn Arg Lys Cys Thr Glu Cys Phe Thr His Ala 500 505 510 Val Glu Ala Ala Glu Phe Leu Ala Ala Thr Ala Ala Lys His Gln Leu 515 520 525 Arg Asn Asp Phe Gln Ile His Ser Val Arg Gly Ile Lys Asn Pro Gly 530 535 540 Asp Glu Asp Asn Gly Glu Pro Pro Ala Asn Val Lys Tyr Val Ile Thr 545 550 555 560 Gly Ile Ile Leu Val Ile Ile Ala Leu Ala Phe Phe Gly Met Val Leu 565 570 575 Ser Thr Gln Arg Lys Arg Ala His Gly Val Thr Trp Phe Pro Glu Gly 580 585 590 Phe Arg Ala Pro Ala Ala Val Met Ser Arg Arg Arg Arg Asp Pro His 595 600 605 Gly Gln Glu Met Arg Asn Leu Asn Lys Gln Val Ala Met Gln Ser Gln 610 615 620 Gly Val Gly Gln Pro Gly Ala His Trp Ser Asp Asp Glu Ser Asp Met 625 630 635 640 Pro Leu Pro Lys Arg Gln Arg Ser Asp Pro Val Ser Gly Val Gly Leu 645 650 655 Gly Asn Asn Gly Gly Tyr Ala Ser Asp His Thr Met Val Ser Glu Tyr 660 665 670 Glu Glu Ala Asp Gln Arg Val Trp Ser Gln Ala His Leu Asp Val Val 675 680 685 Asp Val Arg Ala Ile Met Thr Pro Pro Ala His Gln Asp Gly Gly Lys 690 695 700 His Asp Val Asp Ala Arg Gly Pro Cys Gly Leu Thr Pro Leu Met Ile 705 710 715 720 Ala Ala Val Arg Gly Gly Gly Leu Asp Thr Gly Glu Asp Ile Glu Asn 725 730 735 Asn Glu Asp Ser Thr Ala Gln Val Ile Ser Asp Leu Leu Ala Gln Gly 740 745 750 Ala Glu Leu Asn Ala Thr Met Asp Lys Thr Gly Glu Thr Ser Leu His 755 760 765 Leu Ala Ala Arg Phe Ala Arg Ala Asp Ala Ala Lys Arg Leu Phe His 770 775 780 Ala Gly Ala Asp Ala Asn Cys Gln Asp Asn Thr Gly Arg Thr Pro Leu 785 790 795 800 His Ala Ala Val Ala Ala Asp Ala Met Gly Val Phe Gln Ile Leu Leu 805 810 815 Arg Asn Arg Ala Thr Asn Leu Asn Ala Arg Met His Asp Gly Thr Thr 820 825 830 Pro Leu Ile Leu Ala Ala Arg Leu Ala Ile Glu Gly Met Val Glu Asp 835 840 845 Leu Ile Thr Ala Asp Ala Asp Ile Asn Ala Ala Asp Asn Ser Gly Lys 850 855 860 Thr Ala Leu His Trp Ala Ala Ala Val Asn Asn Thr Glu Ala Val Asn 865 870 875 880 Ile Leu Leu Met His His Ala Asn Arg Asp Ala Gln Asp Asp Lys Asp 885 890 895 Glu Thr Pro Leu Phe Leu Ala Ala Arg Glu Gly Ser Tyr Glu Ala Cys 900 905 910 Lys Ala Leu Leu Asp Asn Phe Ala Asn Arg Glu Ile Thr Asp His Met 915 920 925 Asp Arg Leu Pro Arg Asp Val Ala Ser Glu Arg Leu His His Asp Ile 930 935 940 Val Arg Leu Leu Asp Glu His Val Pro Arg Ser Pro Gln Met Leu Ser 945 950 955 960 Met Thr Pro Gln Ala Met Ile Gly Ser Pro Pro Pro Gly Gln Gln Gln 965 970 975 Pro Gln Leu Ile Thr Gln Pro Thr Val Ile Ser Ala Gly Asn Gly Gly 980 985 990 Asn Asn Gly Asn Gly Asn Ala Ser Gly Lys Gln Ser Asn Gln Thr Ala 995 1000 1005 Lys Gln Lys Ala Ala Lys Lys Ala Lys Leu Ile Glu Gly Ser Pro 1010 1015 1020 Asp Asn Gly Leu Asp Ala Thr Gly Ser Leu Arg Arg Lys Ala Ser 1025 1030 1035 Ser Lys Lys Thr Ser Ala Ala Ser Lys Lys Ala Ala Asn Leu Asn 1040 1045 1050 Gly Leu Asn Pro Gly Gln Leu Thr Gly Gly Val Ser Gly Val Pro 1055 1060 1065 Gly Val Pro Pro Thr Asn Ser Ala Val Gln Ala Ala Ala Ala Ala 1070 1075 1080 Ala Ala Ala Val Ala Ala Met Ser His Glu Leu Glu Gly Ser Pro 1085 1090 1095 Val Gly Val Gly Met Gly Gly Asn Leu Pro Ser Pro Tyr Asp Thr 1100 1105 1110 Ser Ser Met Tyr Ser Asn Ala Met Ala Ala Pro Leu Ala Asn Gly 1115 1120 1125 Asn Pro Asn Thr Gly Ala Lys Gln Pro Pro Ser 1130 1135 

What is claimed is:
 1. A method for the expansion of a human precursor cell comprising contacting the cell with an amount of an agonist of Notch function effective to inhibit differentiation of the cell, and exposing the cell to cell growth conditions such that the cell proliferates.
 2. The method according to claim 1 wherein the precursor cell is of ectodermal origin.
 3. The method according to claim 1 wherein the precursor cell is of endodermal origin.
 4. The method according to claim 1 wherein the precursor cell is of mesodermal origin.
 5. The method according to claim 1 wherein the precursor cell is selected from the group consisting of hematopoietic precursor-cells, epithelial precursor cells, kidney precursor cells, neural precursor cells, skin precursor cells, osteoblast precursor cells, chondrocyte precursor cells, and liver precursor cells.
 6. The method according to claim 1 wherein the agonist is a Delta protein or a derivative thereof which binds to Notch.
 7. The method according to claim 1 wherein the agonist is a Serrate protein or a derivative thereof which binds to Notch.
 8. The method according to claim 1 wherein the agonist is an antibody to a Notch protein or a fragment of the antibody containing the binding region.
 9. The method according to claim 1 wherein the precursor cell is an hematopoietic stem cell.
 10. The method according to claim 1 wherein the precursor cell contains a recombinant nucleic acid encoding a protein of value in the treatment of a human disease or disorder.
 11. The method according to claim 1 wherein the agonist is a Delta or Serrate protein and said contacting is carried out by a method comprising exposing the precursor cells to cells recombinantly expressing the agonist.
 12. The method according to claim 1 wherein said contacting is carried out by culturing said precursor cells in medium containing a purified agonist in soluble form.
 13. The method according to claim 1 wherein substantially no differentiation of the cells occurs.
 14. A method for the expansion of a precursor cell comprising contacting the cell with an amount of a soluble agonist of Notch function effective to inhibit differentiation of the cell, and exposing the cell to cell growth conditions such that the cell proliferates.
 15. The method according to claim 14 wherein the precursor cell is selected from the group consisting of hematopoietic precursor cells, epithelial precursor cells, kidney precursor cells, neural precursor cells, skin precursor cells, osteoblast precursor cells, chondrocyte precursor cells, liver precursor cells, and muscle cells.
 16. The method according to claim 14 wherein the precursor cell is an hematopoietic stem cell.
 17. The method according to claim 14 wherein substantially no differentiation of the cells occurs.
 18. The method according to claim 14 wherein the soluble agonist is a derivative of a Delta protein which binds to a Notch protein.
 19. The method according to claim 14 wherein the soluble agonist is a derivative of a Serrate protein which binds to a Notch protein.
 20. The method according to claim 18 wherein the derivative of Delta consists essentially of the extracellular domain of a Delta protein.
 21. The method according to claim 19 wherein the derivative of Serrate consists essentially of the extracellular domain of a Serrate protein.
 22. The method according to claim 14 wherein the soluble agonist is an antibody to a Notch protein or a fragment of the antibody containing the binding region.
 23. A method for the expansion of a precursor cell comprising recombinantly expressing within the cell an amount of a Deltex protein or fragment thereof which binds to a Notch protein in the precursor cell effective to inhibit differentiation of the cells; and exposing the cell to cell growth conditions such that the cell proliferates.
 24. A method for the expansion of a hematopoietic precursor cell comprising recombinantly expressing within the cell an amount of a Notch protein consisting essentially of the intracellular domain of a Notch protein in the precursor cell effective to inhibit differentiation; and exposing the cell to cell growth conditions such that the cell proliferates.
 25. A method for the expansion of an epithelial precursor cell comprising recombinantly expressing within the cell an amount of a Notch protein consisting essentially of the intracellular domain of a Notch protein in the precursor cell effective to inhibit differentiation; and exposing the cell to cell growth conditions such that the cell proliferates.
 26. A method for the expansion of a liver precursor cell comprising recombinantly expressing within the cell an amount of a Notch protein consisting essentially of the intracellular domain of a Notch protein in the precursor cell effective to inhibit differentiation; and exposing the cell to cell growth conditions such that the cell proliferates.
 27. A method for the expansion of a human precursor cell comprising contacting the precursor cell with a second cell wherein the second cell recombinantly expresses on its surface a molecule consisting of at least the extracellular domain of a Notch ligand; and exposing the precursor cell to cell growth conditions such that the precursor cell proliferates.
 28. The method of claim 27 wherein the second cell recombinantly expresses on its surface at least the extracellular domain of a Delta protein.
 29. The method of claim 27 wherein the second cell recombinantly expresses on its surface at least the extracellular domain of a Serrate protein.
 30. A method for the expansion of an hematopoietic precursor cell comprising contacting the precursor cell with a second cell wherein the second cell recombinantly expresses on its surface a molecule consisting of at least the extracellular domain of a Notch ligand; and exposing the precursor cell to cell growth conditions such that the precursor cell proliferates.
 31. The method according to claim 14 wherein the precursor cell contains a recombinant nucleic acid encoding a protein of value in the treatment of a disease or disorder.
 32. The method according to claim 14 which further comprises after said contacting step the step of introducing into the cell a recombinant nucleic acid encoding a protein of value in the treatment of a disease or disorder.
 33. A method for the expansion of a human precursor cell comprising contacting the precursor cell with an amount of a second cell expressing a Notch ligand effective to inhibit differentiation of the cell; and exposing the precursor cell to cell growth conditions such that the precursor cell proliferates.
 34. A method for therapy comprising contacting a precursor cell with an effective amount of an agonist of Notch function effective to inhibit differentiation of the cell; exposing the cell to cell growth conditions to form an expanded precursor cell population; and administering a therapeutically effective amount of the expanded precursor cell population or progeny cells produced therefrom to a patient.
 35. The method according to claim 1 or 14 which further comprises removing the agonist of Notch function and inducing at least some of the resulting expanded cells to differentiate.
 36. A method for the inhibition of a function of a signaling pathway that regulates cell growth or differentiation comprising contacting a cell with an amount of an agonist of Notch function, effective to inhibit a function of a signaling pathway in the cell that regulates cell growth or differentiation.
 37. The method according to claim 36 wherein the pathway is a ras-mediated pathway.
 38. The method according to claim 36 wherein the pathway is a wnt-1 or homologous locus-mediated pathway.
 39. The method according to claim 1 in which said contacting and exposing steps are carried out concurrently.
 40. A method for promoting mammalian neuronal cell growth comprising contacting a mammalian neuron with an antagonist of Notch function and exposing the neuron to neuronal cell growth conditions.
 41. The method according to claim 1, 14 and 16 in which said contacting and exposing steps are carried out in vitro. 